gecko-dev/content/media/MediaDecoderStateMachine.cpp

/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifdef XP_WIN
// Include Windows headers required for enabling high precision timers.
#include "windows.h"
#include "mmsystem.h"
#endif

#include "mozilla/DebugOnly.h"
#include <stdint.h>

#include "MediaDecoderStateMachine.h"
#include "AudioStream.h"
#include "nsTArray.h"
#include "MediaDecoder.h"
#include "MediaDecoderReader.h"
#include "mozilla/mozalloc.h"
#include "VideoUtils.h"
#include "mozilla/dom/TimeRanges.h"
#include "nsDeque.h"
#include "AudioSegment.h"
#include "VideoSegment.h"
#include "ImageContainer.h"
#include "nsComponentManagerUtils.h"
#include "nsITimer.h"
#include "nsContentUtils.h"
#include "MediaShutdownManager.h"
#include "SharedThreadPool.h"
#include "MediaTaskQueue.h"
#include "nsIEventTarget.h"
#include "prenv.h"
#include "mozilla/Preferences.h"
#include "gfx2DGlue.h"

#include <algorithm>

namespace mozilla {

using namespace mozilla::layers;
using namespace mozilla::dom;
using namespace mozilla::gfx;

#ifdef PR_LOGGING
extern PRLogModuleInfo* gMediaDecoderLog;
#define DECODER_LOG(type, msg) PR_LOG(gMediaDecoderLog, type, msg)
#else
#define DECODER_LOG(type, msg)
#endif

// GetCurrentTime is defined in winbase.h as zero argument macro forwarding to
// GetTickCount() and conflicts with MediaDecoderStateMachine::GetCurrentTime
// implementation.  With unified builds, putting this in headers is not enough.
#ifdef GetCurrentTime
#undef GetCurrentTime
#endif

// Wait this number of seconds when buffering, then leave and play
// as best as we can if the required amount of data hasn't been
// retrieved.
static const uint32_t BUFFERING_WAIT_S = 30;

// If audio queue has less than this many usecs of decoded audio, we won't risk
// trying to decode the video, we'll skip decoding video up to the next
// keyframe. We may increase this value for an individual decoder if we
// encounter video frames which take a long time to decode.
static const uint32_t LOW_AUDIO_USECS = 300000;

// If more than this many usecs of decoded audio is queued, we'll hold off
// decoding more audio. If we increase the low audio threshold (see
// LOW_AUDIO_USECS above) we'll also increase this value to ensure it's not
// less than the low audio threshold.
const int64_t AMPLE_AUDIO_USECS = 1000000;

// When we're only playing audio and we don't have a video stream, we divide
// AMPLE_AUDIO_USECS and LOW_AUDIO_USECS by the following value. This reduces
// the amount of decoded audio we buffer, reducing our memory usage. We only
// need to decode far ahead when we're decoding video using software decoding,
// as otherwise a long video decode could cause an audio underrun.
const int64_t NO_VIDEO_AMPLE_AUDIO_DIVISOR = 8;

// Maximum number of bytes we'll allocate and write at once to the audio
// hardware when the audio stream contains missing frames and we're
// writing silence in order to fill the gap. We limit our silence-writes
// to 32KB in order to avoid allocating an impossibly large chunk of
// memory if we encounter a large chunk of silence.
const uint32_t SILENCE_BYTES_CHUNK = 32 * 1024;

// If we have fewer than LOW_VIDEO_FRAMES decoded frames, and
// we're not "prerolling video", we'll skip the video up to the next keyframe
// which is at or after the current playback position.
static const uint32_t LOW_VIDEO_FRAMES = 1;

// Arbitrary "frame duration" when playing only audio.
static const int AUDIO_DURATION_USECS = 40000;

// If we increase our "low audio threshold" (see LOW_AUDIO_USECS above), we
// use this as a factor in all our calculations. Increasing this will cause
// us to be more likely to increase our low audio threshold, and to
// increase it by more.
static const int THRESHOLD_FACTOR = 2;

// If we have less than this much undecoded data available, we'll consider
// ourselves to be running low on undecoded data. We determine how much
// undecoded data we have remaining using the reader's GetBuffered()
// implementation.
static const int64_t LOW_DATA_THRESHOLD_USECS = 5000000;

// LOW_DATA_THRESHOLD_USECS needs to be greater than AMPLE_AUDIO_USECS, otherwise
// the skip-to-keyframe logic can activate when we're running low on data.
static_assert(LOW_DATA_THRESHOLD_USECS > AMPLE_AUDIO_USECS,
              "LOW_DATA_THRESHOLD_USECS is too small");

// Amount of excess usecs of data to add in to the "should we buffer" calculation.
static const uint32_t EXHAUSTED_DATA_MARGIN_USECS = 60000;

// If we enter buffering within QUICK_BUFFER_THRESHOLD_USECS seconds of starting
// decoding, we'll enter "quick buffering" mode, which exits a lot sooner than
// normal buffering mode. This exists so that if the decode-ahead exhausts the
// downloaded data while decode/playback is just starting up (for example
// after a seek while the media is still playing, or when playing a media
// as soon as it's load started), we won't necessarily stop for 30s and wait
// for buffering. We may actually be able to playback in this case, so exit
// buffering early and try to play. If it turns out we can't play, we'll fall
// back to buffering normally.
static const uint32_t QUICK_BUFFER_THRESHOLD_USECS = 2000000;

// If we're quick buffering, we'll remain in buffering mode while we have less than
// QUICK_BUFFERING_LOW_DATA_USECS of decoded data available.
static const uint32_t QUICK_BUFFERING_LOW_DATA_USECS = 1000000;

// If QUICK_BUFFERING_LOW_DATA_USECS is > AMPLE_AUDIO_USECS, we won't exit
// quick buffering in a timely fashion, as the decode pauses when it
// reaches AMPLE_AUDIO_USECS decoded data, and thus we'll never reach
// QUICK_BUFFERING_LOW_DATA_USECS.
static_assert(QUICK_BUFFERING_LOW_DATA_USECS <= AMPLE_AUDIO_USECS,
              "QUICK_BUFFERING_LOW_DATA_USECS is too large");

// This value has been chosen empirically.
static const uint32_t AUDIOSTREAM_MIN_WRITE_BEFORE_START_USECS = 200000;

// The amount of instability we tollerate in calls to
// MediaDecoderStateMachine::UpdateEstimatedDuration(); changes of duration
// less than this are ignored, as they're assumed to be the result of
// instability in the duration estimation.
static const int64_t ESTIMATED_DURATION_FUZZ_FACTOR_USECS = USECS_PER_S / 2;

static TimeDuration UsecsToDuration(int64_t aUsecs) {
  return TimeDuration::FromMilliseconds(static_cast<double>(aUsecs) / USECS_PER_MS);
}

static int64_t DurationToUsecs(TimeDuration aDuration) {
  return static_cast<int64_t>(aDuration.ToSeconds() * USECS_PER_S);
}

MediaDecoderStateMachine::MediaDecoderStateMachine(MediaDecoder* aDecoder,
                                                   MediaDecoderReader* aReader,
                                                   bool aRealTime) :
  mDecoder(aDecoder),
  mState(DECODER_STATE_DECODING_METADATA),
  mSyncPointInMediaStream(-1),
  mSyncPointInDecodedStream(-1),
  mResetPlayStartTime(false),
  mPlayDuration(0),
  mStartTime(-1),
  mEndTime(-1),
  mSeekTime(0),
  mFragmentEndTime(-1),
  mReader(aReader),
  mCurrentFrameTime(0),
  mAudioStartTime(-1),
  mAudioEndTime(-1),
  mVideoFrameEndTime(-1),
  mVolume(1.0),
  mPlaybackRate(1.0),
  mPreservesPitch(true),
  mBasePosition(0),
  mAmpleVideoFrames(2),
  mLowAudioThresholdUsecs(LOW_AUDIO_USECS),
  mAmpleAudioThresholdUsecs(AMPLE_AUDIO_USECS),
  mDispatchedAudioDecodeTask(false),
  mDispatchedVideoDecodeTask(false),
  mIsReaderIdle(false),
  mAudioCaptured(false),
  mTransportSeekable(true),
  mMediaSeekable(true),
  mPositionChangeQueued(false),
  mAudioCompleted(false),
  mGotDurationFromMetaData(false),
  mDispatchedEventToDecode(false),
  mStopAudioThread(true),
  mQuickBuffering(false),
  mIsRunning(false),
  mRunAgain(false),
  mDispatchedRunEvent(false),
  mDecodeThreadWaiting(false),
  mRealTime(aRealTime),
  mEventManager(aDecoder),
  mLastFrameStatus(MediaDecoderOwner::NEXT_FRAME_UNINITIALIZED)
{
  MOZ_COUNT_CTOR(MediaDecoderStateMachine);
  NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");

  // Only enable realtime mode when "media.realtime_decoder.enabled" is true.
  if (Preferences::GetBool("media.realtime_decoder.enabled", false) == false)
    mRealTime = false;

  mAmpleVideoFrames =
    std::max<uint32_t>(Preferences::GetUint("media.video-queue.default-size", 10), 3);

  mBufferingWait = mRealTime ? 0 : BUFFERING_WAIT_S;
  mLowDataThresholdUsecs = mRealTime ? 0 : LOW_DATA_THRESHOLD_USECS;

  mVideoPrerollFrames = mRealTime ? 0 : mAmpleVideoFrames / 2;
  mAudioPrerollUsecs = mRealTime ? 0 : LOW_AUDIO_USECS * 2;

#ifdef XP_WIN
  // Ensure high precision timers are enabled on Windows, otherwise the state
  // machine thread isn't woken up at reliable intervals to set the next frame,
  // and we drop frames while painting. Note that multiple calls to this
  // function per-process is OK, provided each call is matched by a corresponding
  // timeEndPeriod() call.
  timeBeginPeriod(1);
#endif
}

MediaDecoderStateMachine::~MediaDecoderStateMachine()
{
  MOZ_ASSERT(NS_IsMainThread(), "Should be on main thread.");
  MOZ_COUNT_DTOR(MediaDecoderStateMachine);
  NS_ASSERTION(!mPendingWakeDecoder.get(),
               "WakeDecoder should have been revoked already");

  if (mDecodeTaskQueue) {
    mDecodeTaskQueue->Shutdown();
    mDecodeTaskQueue = nullptr;
  }

  if (mTimer) {
    mTimer->Cancel();
  }
  mTimer = nullptr;
  mReader = nullptr;

#ifdef XP_WIN
  timeEndPeriod(1);
#endif
}

bool MediaDecoderStateMachine::HasFutureAudio() const {
  AssertCurrentThreadInMonitor();
  NS_ASSERTION(HasAudio(), "Should only call HasFutureAudio() when we have audio");
  // We've got audio ready to play if:
  // 1. We've not completed playback of audio, and
  // 2. we either have more than the threshold of decoded audio available, or
  //    we've completely decoded all audio (but not finished playing it yet
  //    as per 1).
  return !mAudioCompleted &&
         (AudioDecodedUsecs() > LOW_AUDIO_USECS * mPlaybackRate || mReader->AudioQueue().IsFinished());
}

bool MediaDecoderStateMachine::HaveNextFrameData() const {
  AssertCurrentThreadInMonitor();
  return (!HasAudio() || HasFutureAudio()) &&
         (!HasVideo() || mReader->VideoQueue().GetSize() > 0);
}

int64_t MediaDecoderStateMachine::GetDecodedAudioDuration() {
  NS_ASSERTION(OnDecodeThread() || OnStateMachineThread(),
               "Should be on decode thread or state machine thread");
  AssertCurrentThreadInMonitor();
  int64_t audioDecoded = mReader->AudioQueue().Duration();
  if (mAudioEndTime != -1) {
    audioDecoded += mAudioEndTime - GetMediaTime();
  }
  return audioDecoded;
}

void MediaDecoderStateMachine::SendStreamAudio(AudioData* aAudio,
                                               DecodedStreamData* aStream,
                                               AudioSegment* aOutput)
{
  NS_ASSERTION(OnDecodeThread() ||
               OnStateMachineThread(), "Should be on decode thread or state machine thread");
  AssertCurrentThreadInMonitor();

  if (aAudio->mTime <= aStream->mLastAudioPacketTime) {
    // ignore packet that we've already processed
    return;
  }
  aStream->mLastAudioPacketTime = aAudio->mTime;
  aStream->mLastAudioPacketEndTime = aAudio->GetEndTime();

  // This logic has to mimic AudioLoop closely to make sure we write
  // the exact same silences
  CheckedInt64 audioWrittenOffset = UsecsToFrames(mInfo.mAudio.mRate,
      aStream->mInitialTime + mStartTime) + aStream->mAudioFramesWritten;
  CheckedInt64 frameOffset = UsecsToFrames(mInfo.mAudio.mRate, aAudio->mTime);
  if (!audioWrittenOffset.isValid() || !frameOffset.isValid())
    return;
  if (audioWrittenOffset.value() < frameOffset.value()) {
    // Write silence to catch up
    DECODER_LOG(PR_LOG_DEBUG, ("%p Decoder writing %d frames of silence to MediaStream",
                               mDecoder.get(), int32_t(frameOffset.value() - audioWrittenOffset.value())));
    AudioSegment silence;
    silence.InsertNullDataAtStart(frameOffset.value() - audioWrittenOffset.value());
    aStream->mAudioFramesWritten += silence.GetDuration();
    aOutput->AppendFrom(&silence);
  }

  int64_t offset;
  if (aStream->mAudioFramesWritten == 0) {
    NS_ASSERTION(frameOffset.value() <= audioWrittenOffset.value(),
                 "Otherwise we'd have taken the write-silence path");
    // We're starting in the middle of a packet. Split the packet.
    offset = audioWrittenOffset.value() - frameOffset.value();
  } else {
    // Write the entire packet.
    offset = 0;
  }

  if (offset >= aAudio->mFrames)
    return;

  aAudio->EnsureAudioBuffer();
  nsRefPtr<SharedBuffer> buffer = aAudio->mAudioBuffer;
  AudioDataValue* bufferData = static_cast<AudioDataValue*>(buffer->Data());
  nsAutoTArray<const AudioDataValue*,2> channels;
  for (uint32_t i = 0; i < aAudio->mChannels; ++i) {
    channels.AppendElement(bufferData + i*aAudio->mFrames + offset);
  }
  aOutput->AppendFrames(buffer.forget(), channels, aAudio->mFrames);
  DECODER_LOG(PR_LOG_DEBUG, ("%p Decoder writing %d frames of data to MediaStream for AudioData at %lld",
                             mDecoder.get(), aAudio->mFrames - int32_t(offset), aAudio->mTime));
  aStream->mAudioFramesWritten += aAudio->mFrames - int32_t(offset);
}

static void WriteVideoToMediaStream(layers::Image* aImage,
                                    int64_t aDuration,
                                    const IntSize& aIntrinsicSize,
                                    VideoSegment* aOutput)
{
  nsRefPtr<layers::Image> image = aImage;
  aOutput->AppendFrame(image.forget(), aDuration, aIntrinsicSize);
}

static const TrackID TRACK_AUDIO = 1;
static const TrackID TRACK_VIDEO = 2;
static const TrackRate RATE_VIDEO = USECS_PER_S;

void MediaDecoderStateMachine::SendStreamData()
{
  NS_ASSERTION(OnDecodeThread() ||
               OnStateMachineThread(), "Should be on decode thread or state machine thread");
  AssertCurrentThreadInMonitor();

  DecodedStreamData* stream = mDecoder->GetDecodedStream();
  if (!stream)
    return;

  if (mState == DECODER_STATE_DECODING_METADATA)
    return;

  // If there's still an audio thread alive, then we can't send any stream
  // data yet since both SendStreamData and the audio thread want to be in
  // charge of popping the audio queue. We're waiting for the audio thread
  // to die before sending anything to our stream.
  if (mAudioThread)
    return;

  int64_t minLastAudioPacketTime = INT64_MAX;
  bool finished =
      (!mInfo.HasAudio() || mReader->AudioQueue().IsFinished()) &&
      (!mInfo.HasVideo() || mReader->VideoQueue().IsFinished());
  if (mDecoder->IsSameOriginMedia()) {
    SourceMediaStream* mediaStream = stream->mStream;
    StreamTime endPosition = 0;

    if (!stream->mStreamInitialized) {
      if (mInfo.HasAudio()) {
        AudioSegment* audio = new AudioSegment();
        mediaStream->AddTrack(TRACK_AUDIO, mInfo.mAudio.mRate, 0, audio);
        stream->mStream->DispatchWhenNotEnoughBuffered(TRACK_AUDIO,
            GetStateMachineThread(), GetWakeDecoderRunnable());
      }
      if (mInfo.HasVideo()) {
        VideoSegment* video = new VideoSegment();
        mediaStream->AddTrack(TRACK_VIDEO, RATE_VIDEO, 0, video);
        stream->mStream->DispatchWhenNotEnoughBuffered(TRACK_VIDEO,
            GetStateMachineThread(), GetWakeDecoderRunnable());
      }
      stream->mStreamInitialized = true;
    }

    if (mInfo.HasAudio()) {
      nsAutoTArray<AudioData*,10> audio;
      // It's OK to hold references to the AudioData because while audio
      // is captured, only the decoder thread pops from the queue (see below).
      mReader->AudioQueue().GetElementsAfter(stream->mLastAudioPacketTime, &audio);
      AudioSegment output;
      for (uint32_t i = 0; i < audio.Length(); ++i) {
        SendStreamAudio(audio[i], stream, &output);
      }
      if (output.GetDuration() > 0) {
        mediaStream->AppendToTrack(TRACK_AUDIO, &output);
      }
      if (mReader->AudioQueue().IsFinished() && !stream->mHaveSentFinishAudio) {
        mediaStream->EndTrack(TRACK_AUDIO);
        stream->mHaveSentFinishAudio = true;
      }
      minLastAudioPacketTime = std::min(minLastAudioPacketTime, stream->mLastAudioPacketTime);
      endPosition = std::max(endPosition,
          TicksToTimeRoundDown(mInfo.mAudio.mRate, stream->mAudioFramesWritten));
    }

    if (mInfo.HasVideo()) {
      nsAutoTArray<VideoData*,10> video;
      // It's OK to hold references to the VideoData only the decoder thread
      // pops from the queue.
      mReader->VideoQueue().GetElementsAfter(stream->mNextVideoTime, &video);
      VideoSegment output;
      for (uint32_t i = 0; i < video.Length(); ++i) {
        VideoData* v = video[i];
        if (stream->mNextVideoTime < v->mTime) {
          DECODER_LOG(PR_LOG_DEBUG, ("%p Decoder writing last video to MediaStream %p for %lldus",
                                     mDecoder.get(), mediaStream,
                                     v->mTime - stream->mNextVideoTime));
          // Write last video frame to catch up. mLastVideoImage can be null here
          // which is fine, it just means there's no video.
          WriteVideoToMediaStream(stream->mLastVideoImage,
            v->mTime - stream->mNextVideoTime, stream->mLastVideoImageDisplaySize,
              &output);
          stream->mNextVideoTime = v->mTime;
        }
        if (stream->mNextVideoTime < v->GetEndTime()) {
          DECODER_LOG(PR_LOG_DEBUG, ("%p Decoder writing video frame %lldus to MediaStream %p for %lldus",
                                     mDecoder.get(), v->mTime, mediaStream,
                                     v->GetEndTime() - stream->mNextVideoTime));
          WriteVideoToMediaStream(v->mImage,
              v->GetEndTime() - stream->mNextVideoTime, v->mDisplay,
              &output);
          stream->mNextVideoTime = v->GetEndTime();
          stream->mLastVideoImage = v->mImage;
          stream->mLastVideoImageDisplaySize = v->mDisplay;
        } else {
          DECODER_LOG(PR_LOG_DEBUG, ("%p Decoder skipping writing video frame %lldus (end %lldus) to MediaStream",
                                     mDecoder.get(), v->mTime, v->GetEndTime()));
        }
      }
      if (output.GetDuration() > 0) {
        mediaStream->AppendToTrack(TRACK_VIDEO, &output);
      }
      if (mReader->VideoQueue().IsFinished() && !stream->mHaveSentFinishVideo) {
        mediaStream->EndTrack(TRACK_VIDEO);
        stream->mHaveSentFinishVideo = true;
      }
      endPosition = std::max(endPosition,
          TicksToTimeRoundDown(RATE_VIDEO, stream->mNextVideoTime - stream->mInitialTime));
    }

    if (!stream->mHaveSentFinish) {
      stream->mStream->AdvanceKnownTracksTime(endPosition);
    }

    if (finished && !stream->mHaveSentFinish) {
      stream->mHaveSentFinish = true;
      stream->mStream->Finish();
    }
  }

  if (mAudioCaptured) {
    // Discard audio packets that are no longer needed.
    while (true) {
      const AudioData* a = mReader->AudioQueue().PeekFront();
      // Packet times are not 100% reliable so this may discard packets that
      // actually contain data for mCurrentFrameTime. This means if someone might
      // create a new output stream and we actually don't have the audio for the
      // very start. That's OK, we'll play silence instead for a brief moment.
      // That's OK. Seeking to this time would have a similar issue for such
      // badly muxed resources.
      if (!a || a->GetEndTime() >= minLastAudioPacketTime)
        break;
      mAudioEndTime = std::max(mAudioEndTime, a->GetEndTime());
      delete mReader->AudioQueue().PopFront();
    }

    if (finished) {
      mAudioCompleted = true;
      UpdateReadyState();
    }
  }
}

MediaDecoderStateMachine::WakeDecoderRunnable*
MediaDecoderStateMachine::GetWakeDecoderRunnable()
{
  AssertCurrentThreadInMonitor();

  if (!mPendingWakeDecoder.get()) {
    mPendingWakeDecoder = new WakeDecoderRunnable(this);
  }
  return mPendingWakeDecoder.get();
}

bool MediaDecoderStateMachine::HaveEnoughDecodedAudio(int64_t aAmpleAudioUSecs)
{
  AssertCurrentThreadInMonitor();

  if (mReader->AudioQueue().GetSize() == 0 ||
      GetDecodedAudioDuration() < aAmpleAudioUSecs) {
    return false;
  }
  if (!mAudioCaptured) {
    return true;
  }

  DecodedStreamData* stream = mDecoder->GetDecodedStream();
  if (stream && stream->mStreamInitialized && !stream->mHaveSentFinishAudio) {
    if (!stream->mStream->HaveEnoughBuffered(TRACK_AUDIO)) {
      return false;
    }
    stream->mStream->DispatchWhenNotEnoughBuffered(TRACK_AUDIO,
        GetStateMachineThread(), GetWakeDecoderRunnable());
  }

  return true;
}

bool MediaDecoderStateMachine::HaveEnoughDecodedVideo()
{
  AssertCurrentThreadInMonitor();

  if (static_cast<uint32_t>(mReader->VideoQueue().GetSize()) < mAmpleVideoFrames * mPlaybackRate) {
    return false;
  }

  DecodedStreamData* stream = mDecoder->GetDecodedStream();
  if (stream && stream->mStreamInitialized && !stream->mHaveSentFinishVideo) {
    if (!stream->mStream->HaveEnoughBuffered(TRACK_VIDEO)) {
      return false;
    }
    stream->mStream->DispatchWhenNotEnoughBuffered(TRACK_VIDEO,
        GetStateMachineThread(), GetWakeDecoderRunnable());
  }

  return true;
}

bool
MediaDecoderStateMachine::NeedToDecodeVideo()
{
  AssertCurrentThreadInMonitor();
  NS_ASSERTION(OnStateMachineThread() || OnDecodeThread(),
               "Should be on state machine or decode thread.");
  return mIsVideoDecoding && !HaveEnoughDecodedVideo();
}

void
MediaDecoderStateMachine::DecodeVideo()
{
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  NS_ASSERTION(OnDecodeThread(), "Should be on decode thread.");

  if (mState != DECODER_STATE_DECODING && mState != DECODER_STATE_BUFFERING) {
    mDispatchedVideoDecodeTask = false;
    return;
  }
  EnsureActive();

  // We don't want to consider skipping to the next keyframe if we've
  // only just started up the decode loop, so wait until we've decoded
  // some frames before enabling the keyframe skip logic on video.
  if (mIsVideoPrerolling &&
      (static_cast<uint32_t>(mReader->VideoQueue().GetSize())
        >= mVideoPrerollFrames * mPlaybackRate))
  {
    mIsVideoPrerolling = false;
  }

  // We'll skip the video decode to the nearest keyframe if we're low on
  // audio, or if we're low on video, provided we're not running low on
  // data to decode. If we're running low on downloaded data to decode,
  // we won't start keyframe skipping, as we'll be pausing playback to buffer
  // soon anyway and we'll want to be able to display frames immediately
  // after buffering finishes.
  if (mState == DECODER_STATE_DECODING &&
      !mSkipToNextKeyFrame &&
      mIsVideoDecoding &&
      ((!mIsAudioPrerolling && mIsAudioDecoding &&
        GetDecodedAudioDuration() < mLowAudioThresholdUsecs * mPlaybackRate) ||
        (!mIsVideoPrerolling && mIsVideoDecoding &&
        (static_cast<uint32_t>(mReader->VideoQueue().GetSize())
          < LOW_VIDEO_FRAMES * mPlaybackRate))) &&
      !HasLowUndecodedData())
  {
    mSkipToNextKeyFrame = true;
    DECODER_LOG(PR_LOG_DEBUG, ("%p Skipping video decode to the next keyframe", mDecoder.get()));
  }

  // Time the video decode, so that if it's slow, we can increase our low
  // audio threshold to reduce the chance of an audio underrun while we're
  // waiting for a video decode to complete.
  TimeDuration decodeTime;
  {
    int64_t currentTime = GetMediaTime();
    ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
    TimeStamp start = TimeStamp::Now();
    mIsVideoDecoding = mReader->DecodeVideoFrame(mSkipToNextKeyFrame, currentTime);
    decodeTime = TimeStamp::Now() - start;
  }
  if (!mIsVideoDecoding) {
    // Playback ended for this stream, close the sample queue.
    mReader->VideoQueue().Finish();
    CheckIfDecodeComplete();
  }

  if (THRESHOLD_FACTOR * DurationToUsecs(decodeTime) > mLowAudioThresholdUsecs &&
      !HasLowUndecodedData())
  {
    mLowAudioThresholdUsecs =
      std::min(THRESHOLD_FACTOR * DurationToUsecs(decodeTime), AMPLE_AUDIO_USECS);
    mAmpleAudioThresholdUsecs = std::max(THRESHOLD_FACTOR * mLowAudioThresholdUsecs,
                                          mAmpleAudioThresholdUsecs);
    DECODER_LOG(PR_LOG_DEBUG,
                ("Slow video decode, set mLowAudioThresholdUsecs=%lld mAmpleAudioThresholdUsecs=%lld",
                mLowAudioThresholdUsecs, mAmpleAudioThresholdUsecs));
  }

  SendStreamData();

  // The ready state can change when we've decoded data, so update the
  // ready state, so that DOM events can fire.
  UpdateReadyState();

  mDispatchedVideoDecodeTask = false;
  DispatchDecodeTasksIfNeeded();
}

bool
MediaDecoderStateMachine::NeedToDecodeAudio()
{
  AssertCurrentThreadInMonitor();
  NS_ASSERTION(OnStateMachineThread() || OnDecodeThread(),
               "Should be on state machine or decode thread.");
  return mIsAudioDecoding &&
         !HaveEnoughDecodedAudio(mAmpleAudioThresholdUsecs * mPlaybackRate);
}

void
MediaDecoderStateMachine::DecodeAudio()
{
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  NS_ASSERTION(OnDecodeThread(), "Should be on decode thread.");

  if (mState != DECODER_STATE_DECODING && mState != DECODER_STATE_BUFFERING) {
    mDispatchedAudioDecodeTask = false;
    return;
  }
  EnsureActive();

  // We don't want to consider skipping to the next keyframe if we've
  // only just started up the decode loop, so wait until we've decoded
  // some audio data before enabling the keyframe skip logic on audio.
  if (mIsAudioPrerolling &&
      GetDecodedAudioDuration() >= mAudioPrerollUsecs * mPlaybackRate) {
    mIsAudioPrerolling = false;
  }

  {
    ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
    mIsAudioDecoding = mReader->DecodeAudioData();
  }
  if (!mIsAudioDecoding) {
    // Playback ended for this stream, close the sample queue.
    mReader->AudioQueue().Finish();
    CheckIfDecodeComplete();
  }

  SendStreamData();

  // Notify to ensure that the AudioLoop() is not waiting, in case it was
  // waiting for more audio to be decoded.
  mDecoder->GetReentrantMonitor().NotifyAll();

  // The ready state can change when we've decoded data, so update the
  // ready state, so that DOM events can fire.
  UpdateReadyState();

  mDispatchedAudioDecodeTask = false;
  DispatchDecodeTasksIfNeeded();
}

void
MediaDecoderStateMachine::CheckIfDecodeComplete()
{
  AssertCurrentThreadInMonitor();
  if (mState == DECODER_STATE_SHUTDOWN ||
      mState == DECODER_STATE_SEEKING ||
      mState == DECODER_STATE_COMPLETED) {
    // Don't change our state if we've already been shutdown, or we're seeking,
    // since we don't want to abort the shutdown or seek processes.
    return;
  }
  MOZ_ASSERT(!mReader->AudioQueue().IsFinished() || !mIsAudioDecoding);
  MOZ_ASSERT(!mReader->VideoQueue().IsFinished() || !mIsVideoDecoding);
  if (!mIsVideoDecoding && !mIsAudioDecoding) {
    // We've finished decoding all active streams,
    // so move to COMPLETED state.
    mState = DECODER_STATE_COMPLETED;
    DispatchDecodeTasksIfNeeded();
    ScheduleStateMachine();
  }
  DECODER_LOG(PR_LOG_DEBUG,
    ("%p CheckIfDecodeComplete %scompleted", mDecoder.get(),
    ((mState == DECODER_STATE_COMPLETED) ? "" : "NOT ")));
}

bool MediaDecoderStateMachine::IsPlaying()
{
  AssertCurrentThreadInMonitor();

  return !mPlayStartTime.IsNull();
}

// If we have already written enough frames to the AudioStream, start the
// playback.
static void
StartAudioStreamPlaybackIfNeeded(AudioStream* aStream)
{
  // We want to have enough data in the buffer to start the stream.
  if (static_cast<double>(aStream->GetWritten()) / aStream->GetRate() >=
      static_cast<double>(AUDIOSTREAM_MIN_WRITE_BEFORE_START_USECS) / USECS_PER_S) {
    aStream->Start();
  }
}

static void WriteSilence(AudioStream* aStream, uint32_t aFrames)
{
  uint32_t numSamples = aFrames * aStream->GetChannels();
  nsAutoTArray<AudioDataValue, 1000> buf;
  buf.SetLength(numSamples);
  memset(buf.Elements(), 0, numSamples * sizeof(AudioDataValue));
  aStream->Write(buf.Elements(), aFrames);

  StartAudioStreamPlaybackIfNeeded(aStream);
}

void MediaDecoderStateMachine::AudioLoop()
{
  NS_ASSERTION(OnAudioThread(), "Should be on audio thread.");
  DECODER_LOG(PR_LOG_DEBUG, ("%p Begun audio thread/loop", mDecoder.get()));
  int64_t audioDuration = 0;
  int64_t audioStartTime = -1;
  uint32_t channels, rate;
  double volume = -1;
  bool setVolume;
  double playbackRate = -1;
  bool setPlaybackRate;
  bool preservesPitch;
  bool setPreservesPitch;
  AudioChannelType audioChannelType;

  {
    ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
    mAudioCompleted = false;
    audioStartTime = mAudioStartTime;
    NS_ASSERTION(audioStartTime != -1, "Should have audio start time by now");
    channels = mInfo.mAudio.mChannels;
    rate = mInfo.mAudio.mRate;

    audioChannelType = mDecoder->GetAudioChannelType();
    volume = mVolume;
    preservesPitch = mPreservesPitch;
    playbackRate = mPlaybackRate;
  }

  {
    // AudioStream initialization can block for extended periods in unusual
    // circumstances, so we take care to drop the decoder monitor while
    // initializing.
    nsAutoPtr<AudioStream> audioStream(new AudioStream());
    audioStream->Init(channels, rate, audioChannelType, AudioStream::HighLatency);
    audioStream->SetVolume(volume);
    if (audioStream->SetPreservesPitch(preservesPitch) != NS_OK) {
      NS_WARNING("Setting the pitch preservation failed at AudioLoop start.");
    }
    if (playbackRate != 1.0) {
      NS_ASSERTION(playbackRate != 0,
                   "Don't set the playbackRate to 0 on an AudioStream.");
      if (audioStream->SetPlaybackRate(playbackRate) != NS_OK) {
        NS_WARNING("Setting the playback rate failed at AudioLoop start.");
      }
    }

    {
      ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
      mAudioStream = audioStream;
    }
  }

  while (1) {
    // Wait while we're not playing, and we're not shutting down, or we're
    // playing and we've got no audio to play.
    {
      ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
      NS_ASSERTION(mState != DECODER_STATE_DECODING_METADATA,
                   "Should have meta data before audio started playing.");
      while (mState != DECODER_STATE_SHUTDOWN &&
             !mStopAudioThread &&
             (!IsPlaying() ||
              mState == DECODER_STATE_BUFFERING ||
              (mReader->AudioQueue().GetSize() == 0 &&
               !mReader->AudioQueue().AtEndOfStream())))
      {
        if (!IsPlaying() && !mAudioStream->IsPaused()) {
          mAudioStream->Pause();
        }
        mon.Wait();
      }

      // If we're shutting down, break out and exit the audio thread.
      // Also break out if audio is being captured.
      if (mState == DECODER_STATE_SHUTDOWN ||
          mStopAudioThread ||
          mReader->AudioQueue().AtEndOfStream())
      {
        break;
      }

      // We only want to go to the expense of changing the volume if
      // the volume has changed.
      setVolume = volume != mVolume;
      volume = mVolume;

      // Same for the playbackRate.
      setPlaybackRate = playbackRate != mPlaybackRate;
      playbackRate = mPlaybackRate;

      // Same for the pitch preservation.
      setPreservesPitch = preservesPitch != mPreservesPitch;
      preservesPitch = mPreservesPitch;

      if (IsPlaying() && mAudioStream->IsPaused()) {
        mAudioStream->Resume();
      }
    }

    if (setVolume) {
      mAudioStream->SetVolume(volume);
    }
    if (setPlaybackRate) {
      NS_ASSERTION(playbackRate != 0,
                   "Don't set the playbackRate to 0 in the AudioStreams");
      if (mAudioStream->SetPlaybackRate(playbackRate) != NS_OK) {
        NS_WARNING("Setting the playback rate failed in AudioLoop.");
      }
    }
    if (setPreservesPitch) {
      if (mAudioStream->SetPreservesPitch(preservesPitch) != NS_OK) {
        NS_WARNING("Setting the pitch preservation failed in AudioLoop.");
      }
    }
    NS_ASSERTION(mReader->AudioQueue().GetSize() > 0,
                 "Should have data to play");
    // See if there's a gap in the audio. If there is, push silence into the
    // audio hardware, so we can play across the gap.
    const AudioData* s = mReader->AudioQueue().PeekFront();

    // Calculate the number of frames that have been pushed onto the audio
    // hardware.
    CheckedInt64 playedFrames = UsecsToFrames(audioStartTime, rate) +
                                              audioDuration;
    // Calculate the timestamp of the next chunk of audio in numbers of
    // samples.
    CheckedInt64 sampleTime = UsecsToFrames(s->mTime, rate);
    CheckedInt64 missingFrames = sampleTime - playedFrames;
    if (!missingFrames.isValid() || !sampleTime.isValid()) {
      NS_WARNING("Int overflow adding in AudioLoop()");
      break;
    }

    int64_t framesWritten = 0;
    if (missingFrames.value() > 0) {
      // The next audio chunk begins some time after the end of the last chunk
      // we pushed to the audio hardware. We must push silence into the audio
      // hardware so that the next audio chunk begins playback at the correct
      // time.
      missingFrames = std::min<int64_t>(UINT32_MAX, missingFrames.value());
      DECODER_LOG(PR_LOG_DEBUG, ("%p Decoder playing %d frames of silence",
                                 mDecoder.get(), int32_t(missingFrames.value())));
      framesWritten = PlaySilence(static_cast<uint32_t>(missingFrames.value()),
                                  channels, playedFrames.value());
    } else {
      framesWritten = PlayFromAudioQueue(sampleTime.value(), channels);
    }
    audioDuration += framesWritten;
    {
      ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
      CheckedInt64 playedUsecs = FramesToUsecs(audioDuration, rate) + audioStartTime;
      if (!playedUsecs.isValid()) {
        NS_WARNING("Int overflow calculating audio end time");
        break;
      }
      mAudioEndTime = playedUsecs.value();
    }
  }
  {
    ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
    if (mReader->AudioQueue().AtEndOfStream() &&
        mState != DECODER_STATE_SHUTDOWN &&
        !mStopAudioThread)
    {
      // If the media was too short to trigger the start of the audio stream,
      // start it now.
      mAudioStream->Start();
      // Last frame pushed to audio hardware, wait for the audio to finish,
      // before the audio thread terminates.
      bool seeking = false;
      {
        int64_t oldPosition = -1;
        int64_t position = GetMediaTime();
        while (oldPosition != position &&
               mAudioEndTime - position > 0 &&
               mState != DECODER_STATE_SEEKING &&
               mState != DECODER_STATE_SHUTDOWN)
        {
          const int64_t DRAIN_BLOCK_USECS = 100000;
          Wait(std::min(mAudioEndTime - position, DRAIN_BLOCK_USECS));
          oldPosition = position;
          position = GetMediaTime();
        }
        seeking = mState == DECODER_STATE_SEEKING;
      }

      if (!seeking && !mAudioStream->IsPaused()) {
        {
          ReentrantMonitorAutoExit exit(mDecoder->GetReentrantMonitor());
          mAudioStream->Drain();
        }
        // Fire one last event for any extra frames that didn't fill a framebuffer.
        mEventManager.Drain(mAudioEndTime);
      }
    }
  }
  DECODER_LOG(PR_LOG_DEBUG, ("%p Reached audio stream end.", mDecoder.get()));
  {
    // Must hold lock while shutting down and anulling the audio stream to prevent
    // state machine thread trying to use it while we're destroying it.
    ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
    mAudioStream->Shutdown();
    mAudioStream = nullptr;
    mEventManager.Clear();
    if (!mAudioCaptured) {
      mAudioCompleted = true;
      UpdateReadyState();
      // Kick the decode thread; it may be sleeping waiting for this to finish.
      mDecoder->GetReentrantMonitor().NotifyAll();
    }
  }

  DECODER_LOG(PR_LOG_DEBUG, ("%p Audio stream finished playing, audio thread exit", mDecoder.get()));
}

uint32_t MediaDecoderStateMachine::PlaySilence(uint32_t aFrames,
                                                   uint32_t aChannels,
                                                   uint64_t aFrameOffset)

{
  NS_ASSERTION(OnAudioThread(), "Only call on audio thread.");
  NS_ASSERTION(!mAudioStream->IsPaused(), "Don't play when paused");
  uint32_t maxFrames = SILENCE_BYTES_CHUNK / aChannels / sizeof(AudioDataValue);
  uint32_t frames = std::min(aFrames, maxFrames);
  WriteSilence(mAudioStream, frames);
  // Dispatch events to the DOM for the audio just written.
  mEventManager.QueueWrittenAudioData(nullptr, frames * aChannels,
                                      (aFrameOffset + frames) * aChannels);
  return frames;
}

uint32_t MediaDecoderStateMachine::PlayFromAudioQueue(uint64_t aFrameOffset,
                                                      uint32_t aChannels)
{
  NS_ASSERTION(OnAudioThread(), "Only call on audio thread.");
  NS_ASSERTION(!mAudioStream->IsPaused(), "Don't play when paused");
  nsAutoPtr<AudioData> audio(mReader->AudioQueue().PopFront());
  {
    ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
    NS_WARN_IF_FALSE(IsPlaying(), "Should be playing");
    // Awaken the decode loop if it's waiting for space to free up in the
    // audio queue.
    mDecoder->GetReentrantMonitor().NotifyAll();
  }
  int64_t offset = -1;
  uint32_t frames = 0;
  if (!PR_GetEnv("MOZ_QUIET")) {
    DECODER_LOG(PR_LOG_DEBUG, ("%p Decoder playing %d frames of data to stream for AudioData at %lld",
                               mDecoder.get(), audio->mFrames, audio->mTime));
  }
  mAudioStream->Write(audio->mAudioData,
                      audio->mFrames);

  aChannels = mAudioStream->GetOutChannels();

  StartAudioStreamPlaybackIfNeeded(mAudioStream);

  offset = audio->mOffset;
  frames = audio->mFrames;

  // Dispatch events to the DOM for the audio just written.
  mEventManager.QueueWrittenAudioData(audio->mAudioData.get(),
                                      audio->mFrames * aChannels,
                                      (aFrameOffset + frames) * aChannels);
  if (offset != -1) {
    mDecoder->UpdatePlaybackOffset(offset);
  }
  return frames;
}

nsresult MediaDecoderStateMachine::Init(MediaDecoderStateMachine* aCloneDonor)
{
  MOZ_ASSERT(NS_IsMainThread());

  RefPtr<SharedThreadPool> decodePool(
    SharedThreadPool::Get(NS_LITERAL_CSTRING("Media Decode"),
                          Preferences::GetUint("media.num-decode-threads", 25)));
  NS_ENSURE_TRUE(decodePool, NS_ERROR_FAILURE);

  RefPtr<SharedThreadPool> stateMachinePool(
    SharedThreadPool::Get(NS_LITERAL_CSTRING("Media State Machine"), 1));
  NS_ENSURE_TRUE(stateMachinePool, NS_ERROR_FAILURE);

  mDecodeTaskQueue = new MediaTaskQueue(decodePool.forget());
  NS_ENSURE_TRUE(mDecodeTaskQueue, NS_ERROR_FAILURE);

  MediaDecoderReader* cloneReader = nullptr;
  if (aCloneDonor) {
    cloneReader = static_cast<MediaDecoderStateMachine*>(aCloneDonor)->mReader;
  }

  mStateMachineThreadPool = stateMachinePool;

  return mReader->Init(cloneReader);
}

void MediaDecoderStateMachine::StopPlayback()
{
  DECODER_LOG(PR_LOG_DEBUG, ("%p StopPlayback()", mDecoder.get()));

  AssertCurrentThreadInMonitor();

  mDecoder->NotifyPlaybackStopped();

  if (IsPlaying()) {
    mPlayDuration = GetClock();
    mPlayStartTime = TimeStamp();
  }
  // Notify the audio thread, so that it notices that we've stopped playing,
  // so it can pause audio playback.
  mDecoder->GetReentrantMonitor().NotifyAll();
  NS_ASSERTION(!IsPlaying(), "Should report not playing at end of StopPlayback()");
  mDecoder->UpdateStreamBlockingForStateMachinePlaying();

  DispatchDecodeTasksIfNeeded();
}

void MediaDecoderStateMachine::SetSyncPointForMediaStream()
{
  AssertCurrentThreadInMonitor();

  DecodedStreamData* stream = mDecoder->GetDecodedStream();
  if (!stream) {
    return;
  }

  mSyncPointInMediaStream = stream->GetLastOutputTime();
  mSyncPointInDecodedStream = mStartTime + mPlayDuration;
}

int64_t MediaDecoderStateMachine::GetCurrentTimeViaMediaStreamSync()
{
  AssertCurrentThreadInMonitor();
  NS_ASSERTION(mSyncPointInDecodedStream >= 0, "Should have set up sync point");
  DecodedStreamData* stream = mDecoder->GetDecodedStream();
  StreamTime streamDelta = stream->GetLastOutputTime() - mSyncPointInMediaStream;
  return mSyncPointInDecodedStream + MediaTimeToMicroseconds(streamDelta);
}

void MediaDecoderStateMachine::StartPlayback()
{
  DECODER_LOG(PR_LOG_DEBUG, ("%p StartPlayback()", mDecoder.get()));

  NS_ASSERTION(!IsPlaying(), "Shouldn't be playing when StartPlayback() is called");
  AssertCurrentThreadInMonitor();

  mDecoder->NotifyPlaybackStarted();
  mPlayStartTime = TimeStamp::Now();

  NS_ASSERTION(IsPlaying(), "Should report playing by end of StartPlayback()");
  if (NS_FAILED(StartAudioThread())) {
    NS_WARNING("Failed to create audio thread");
  }
  mDecoder->GetReentrantMonitor().NotifyAll();
  mDecoder->UpdateStreamBlockingForStateMachinePlaying();
}

void MediaDecoderStateMachine::UpdatePlaybackPositionInternal(int64_t aTime)
{
  NS_ASSERTION(OnStateMachineThread() || OnDecodeThread(),
               "Should be on state machine thread.");
  AssertCurrentThreadInMonitor();

  NS_ASSERTION(mStartTime >= 0, "Should have positive mStartTime");
  mCurrentFrameTime = aTime - mStartTime;
  NS_ASSERTION(mCurrentFrameTime >= 0, "CurrentTime should be positive!");
  if (aTime > mEndTime) {
    NS_ASSERTION(mCurrentFrameTime > GetDuration(),
                 "CurrentTime must be after duration if aTime > endTime!");
    mEndTime = aTime;
    nsCOMPtr<nsIRunnable> event =
      NS_NewRunnableMethod(mDecoder, &MediaDecoder::DurationChanged);
    NS_DispatchToMainThread(event, NS_DISPATCH_NORMAL);
  }
}

void MediaDecoderStateMachine::UpdatePlaybackPosition(int64_t aTime)
{
  UpdatePlaybackPositionInternal(aTime);

  bool fragmentEnded = mFragmentEndTime >= 0 && GetMediaTime() >= mFragmentEndTime;
  if (!mPositionChangeQueued || fragmentEnded) {
    mPositionChangeQueued = true;
    nsCOMPtr<nsIRunnable> event =
      NS_NewRunnableMethod(mDecoder, &MediaDecoder::PlaybackPositionChanged);
    NS_DispatchToMainThread(event, NS_DISPATCH_NORMAL);
  }

  // Notify DOM of any queued up audioavailable events
  mEventManager.DispatchPendingEvents(GetMediaTime());

  mMetadataManager.DispatchMetadataIfNeeded(mDecoder, aTime);

  if (fragmentEnded) {
    StopPlayback();
  }
}

void MediaDecoderStateMachine::ClearPositionChangeFlag()
{
  NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");
  AssertCurrentThreadInMonitor();

  mPositionChangeQueued = false;
}

MediaDecoderOwner::NextFrameStatus MediaDecoderStateMachine::GetNextFrameStatus()
{
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  if (IsBuffering() || IsSeeking()) {
    return MediaDecoderOwner::NEXT_FRAME_UNAVAILABLE_BUFFERING;
  } else if (HaveNextFrameData()) {
    return MediaDecoderOwner::NEXT_FRAME_AVAILABLE;
  }
  return MediaDecoderOwner::NEXT_FRAME_UNAVAILABLE;
}

void MediaDecoderStateMachine::SetVolume(double volume)
{
  NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  mVolume = volume;
}

void MediaDecoderStateMachine::SetAudioCaptured(bool aCaptured)
{
  NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  if (!mAudioCaptured && aCaptured && !mStopAudioThread) {
    // Make sure the state machine runs as soon as possible. That will
    // stop the audio thread.
    // If mStopAudioThread is true then we're already stopping the audio thread
    // and since we set mAudioCaptured to true, nothing can start it again.
    ScheduleStateMachine();
  }
  mAudioCaptured = aCaptured;
}

double MediaDecoderStateMachine::GetCurrentTime() const
{
  NS_ASSERTION(NS_IsMainThread() ||
               OnStateMachineThread() ||
               OnDecodeThread(),
               "Should be on main, decode, or state machine thread.");

  return static_cast<double>(mCurrentFrameTime) / static_cast<double>(USECS_PER_S);
}

int64_t MediaDecoderStateMachine::GetDuration()
{
  AssertCurrentThreadInMonitor();

  if (mEndTime == -1 || mStartTime == -1)
    return -1;
  return mEndTime - mStartTime;
}

void MediaDecoderStateMachine::SetDuration(int64_t aDuration)
{
  NS_ASSERTION(NS_IsMainThread() || OnDecodeThread(),
               "Should be on main or decode thread.");
  AssertCurrentThreadInMonitor();

  if (aDuration == -1) {
    return;
  }

  if (mStartTime != -1) {
    mEndTime = mStartTime + aDuration;
  } else {
    mStartTime = 0;
    mEndTime = aDuration;
  }
}

void MediaDecoderStateMachine::UpdateEstimatedDuration(int64_t aDuration)
{
  AssertCurrentThreadInMonitor();
  int64_t duration = GetDuration();
  if (aDuration != duration &&
      abs(aDuration - duration) > ESTIMATED_DURATION_FUZZ_FACTOR_USECS) {
    SetDuration(aDuration);
    nsCOMPtr<nsIRunnable> event =
      NS_NewRunnableMethod(mDecoder, &MediaDecoder::DurationChanged);
    NS_DispatchToMainThread(event, NS_DISPATCH_NORMAL);
  }
}

void MediaDecoderStateMachine::SetMediaEndTime(int64_t aEndTime)
{
  NS_ASSERTION(OnDecodeThread(), "Should be on decode thread");
  AssertCurrentThreadInMonitor();

  mEndTime = aEndTime;
}

void MediaDecoderStateMachine::SetFragmentEndTime(int64_t aEndTime)
{
  AssertCurrentThreadInMonitor();

  mFragmentEndTime = aEndTime < 0 ? aEndTime : aEndTime + mStartTime;
}

void MediaDecoderStateMachine::SetTransportSeekable(bool aTransportSeekable)
{
  NS_ASSERTION(NS_IsMainThread() || OnDecodeThread(),
      "Should be on main thread or the decoder thread.");
  AssertCurrentThreadInMonitor();

  mTransportSeekable = aTransportSeekable;
}

void MediaDecoderStateMachine::SetMediaSeekable(bool aMediaSeekable)
{
  NS_ASSERTION(NS_IsMainThread() || OnDecodeThread(),
      "Should be on main thread or the decoder thread.");

  mMediaSeekable = aMediaSeekable;
}

bool MediaDecoderStateMachine::IsDormantNeeded()
{
  return mReader->IsDormantNeeded();
}

void MediaDecoderStateMachine::SetDormant(bool aDormant)
{
  NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");
  AssertCurrentThreadInMonitor();

  if (!mReader) {
    return;
  }

  if (aDormant) {
    ScheduleStateMachine();
    mState = DECODER_STATE_DORMANT;
    mDecoder->GetReentrantMonitor().NotifyAll();
  } else if ((aDormant != true) && (mState == DECODER_STATE_DORMANT)) {
    ScheduleStateMachine();
    mStartTime = 0;
    mCurrentFrameTime = 0;
    mState = DECODER_STATE_DECODING_METADATA;
    mDecoder->GetReentrantMonitor().NotifyAll();
  }
}

void MediaDecoderStateMachine::Shutdown()
{
  NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");

  // Once we've entered the shutdown state here there's no going back.
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());

  // Change state before issuing shutdown request to threads so those
  // threads can start exiting cleanly during the Shutdown call.
  DECODER_LOG(PR_LOG_DEBUG, ("%p Changed state to SHUTDOWN", mDecoder.get()));
  ScheduleStateMachine();
  mState = DECODER_STATE_SHUTDOWN;
  mDecoder->GetReentrantMonitor().NotifyAll();
}

void MediaDecoderStateMachine::StartDecoding()
{
  NS_ASSERTION(OnStateMachineThread() || OnDecodeThread(),
               "Should be on state machine or decode thread.");
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  if (mState == DECODER_STATE_DECODING) {
    return;
  }
  mState = DECODER_STATE_DECODING;

  mDecodeStartTime = TimeStamp::Now();

  // Reset our "stream finished decoding" flags, so we try to decode all
  // streams that we have when we start decoding.
  mIsVideoDecoding = HasVideo() && !mReader->VideoQueue().IsFinished();
  mIsAudioDecoding = HasAudio() && !mReader->AudioQueue().IsFinished();

  CheckIfDecodeComplete();
  if (mState == DECODER_STATE_COMPLETED) {
    return;
  }

  // Reset other state to pristine values before starting decode.
  mSkipToNextKeyFrame = false;
  mIsAudioPrerolling = true;
  mIsVideoPrerolling = true;

  // Ensure that we've got tasks enqueued to decode data if we need to.
  DispatchDecodeTasksIfNeeded();

  ScheduleStateMachine();
}

void MediaDecoderStateMachine::StartWaitForResources()
{
  NS_ASSERTION(OnStateMachineThread() || OnDecodeThread(),
               "Should be on state machine or decode thread.");
  AssertCurrentThreadInMonitor();
  mState = DECODER_STATE_WAIT_FOR_RESOURCES;
}

void MediaDecoderStateMachine::NotifyWaitingForResourcesStatusChanged()
{
  AssertCurrentThreadInMonitor();
  if (mState != DECODER_STATE_WAIT_FOR_RESOURCES ||
      mReader->IsWaitingMediaResources()) {
    return;
  }
  // The reader is no longer waiting for resources (say a hardware decoder),
  // we can now proceed to decode metadata.
  mState = DECODER_STATE_DECODING_METADATA;
  EnqueueDecodeMetadataTask();
}

void MediaDecoderStateMachine::Play()
{
  NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");
  // When asked to play, switch to decoding state only if
  // we are currently buffering. In other cases, we'll start playing anyway
  // when the state machine notices the decoder's state change to PLAYING.
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  if (mState == DECODER_STATE_BUFFERING) {
    DECODER_LOG(PR_LOG_DEBUG, ("%p Changed state from BUFFERING to DECODING", mDecoder.get()));
    mState = DECODER_STATE_DECODING;
    mDecodeStartTime = TimeStamp::Now();
  }
  ScheduleStateMachine();
}

void MediaDecoderStateMachine::ResetPlayback()
{
  NS_ASSERTION(OnDecodeThread(), "Should be on decode thread.");
  mVideoFrameEndTime = -1;
  mAudioStartTime = -1;
  mAudioEndTime = -1;
  mAudioCompleted = false;
}

void MediaDecoderStateMachine::NotifyDataArrived(const char* aBuffer,
                                                     uint32_t aLength,
                                                     int64_t aOffset)
{
  NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");
  mReader->NotifyDataArrived(aBuffer, aLength, aOffset);

  // While playing an unseekable stream of unknown duration, mEndTime is
  // updated (in AdvanceFrame()) as we play. But if data is being downloaded
  // faster than played, mEndTime won't reflect the end of playable data
  // since we haven't played the frame at the end of buffered data. So update
  // mEndTime here as new data is downloaded to prevent such a lag.
  dom::TimeRanges buffered;
  if (mDecoder->IsInfinite() &&
      NS_SUCCEEDED(mDecoder->GetBuffered(&buffered)))
  {
    uint32_t length = 0;
    buffered.GetLength(&length);
    if (length) {
      double end = 0;
      buffered.End(length - 1, &end);
      ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
      mEndTime = std::max<int64_t>(mEndTime, end * USECS_PER_S);
    }
  }
}

void MediaDecoderStateMachine::Seek(double aTime)
{
  NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());

  // We need to be able to seek both at a transport level and at a media level
  // to seek.
  if (!mMediaSeekable) {
    return;
  }
  // MediaDecoder::mPlayState should be SEEKING while we seek, and
  // in that case MediaDecoder shouldn't be calling us.
  NS_ASSERTION(mState != DECODER_STATE_SEEKING,
               "We shouldn't already be seeking");
  NS_ASSERTION(mState >= DECODER_STATE_DECODING,
               "We should have loaded metadata");
  double t = aTime * static_cast<double>(USECS_PER_S);
  if (t > INT64_MAX) {
    // Prevent integer overflow.
    return;
  }

  mSeekTime = static_cast<int64_t>(t) + mStartTime;
  NS_ASSERTION(mSeekTime >= mStartTime && mSeekTime <= mEndTime,
               "Can only seek in range [0,duration]");

  // Bound the seek time to be inside the media range.
  NS_ASSERTION(mStartTime != -1, "Should know start time by now");
  NS_ASSERTION(mEndTime != -1, "Should know end time by now");
  mSeekTime = std::min(mSeekTime, mEndTime);
  mSeekTime = std::max(mStartTime, mSeekTime);
  mBasePosition = mSeekTime - mStartTime;
  DECODER_LOG(PR_LOG_DEBUG, ("%p Changed state to SEEKING (to %f)", mDecoder.get(), aTime));
  mState = DECODER_STATE_SEEKING;
  if (mDecoder->GetDecodedStream()) {
    mDecoder->RecreateDecodedStream(mSeekTime - mStartTime);
  }
  ScheduleStateMachine();
}

void MediaDecoderStateMachine::StopAudioThread()
{
  NS_ASSERTION(OnDecodeThread() ||
               OnStateMachineThread(), "Should be on decode thread or state machine thread");
  AssertCurrentThreadInMonitor();

  if (mStopAudioThread) {
    // Nothing to do, since the thread is already stopping
    return;
  }

  mStopAudioThread = true;
  mDecoder->GetReentrantMonitor().NotifyAll();
  if (mAudioThread) {
    DECODER_LOG(PR_LOG_DEBUG, ("%p Shutdown audio thread", mDecoder.get()));
    {
      ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
      mAudioThread->Shutdown();
    }
    mAudioThread = nullptr;
    // Now that the audio thread is dead, try sending data to our MediaStream(s).
    // That may have been waiting for the audio thread to stop.
    SendStreamData();
  }
}

nsresult
MediaDecoderStateMachine::EnqueueDecodeMetadataTask()
{
  AssertCurrentThreadInMonitor();

  if (mState != DECODER_STATE_DECODING_METADATA) {
    return NS_OK;
  }
  nsresult rv = mDecodeTaskQueue->Dispatch(
    NS_NewRunnableMethod(this, &MediaDecoderStateMachine::CallDecodeMetadata));
  NS_ENSURE_SUCCESS(rv, rv);

  return NS_OK;
}

void
MediaDecoderStateMachine::EnsureActive()
{
  AssertCurrentThreadInMonitor();
  MOZ_ASSERT(OnDecodeThread());
  if (!mIsReaderIdle) {
    return;
  }
  mIsReaderIdle = false;
  {
    ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
    SetReaderActive();
  }
}

void
MediaDecoderStateMachine::SetReaderIdle()
{
  DECODER_LOG(PR_LOG_DEBUG, ("%p SetReaderIdle()", mDecoder.get()));
  MOZ_ASSERT(OnDecodeThread());
  mReader->SetIdle();
}

void
MediaDecoderStateMachine::SetReaderActive()
{
  DECODER_LOG(PR_LOG_DEBUG, ("%p SetReaderActive()", mDecoder.get()));
  MOZ_ASSERT(OnDecodeThread());
  mReader->SetActive();
}

void
MediaDecoderStateMachine::DispatchDecodeTasksIfNeeded()
{
  AssertCurrentThreadInMonitor();

  // NeedToDecodeAudio() can go from false to true while we hold the
  // monitor, but it can't go from true to false. This can happen because
  // NeedToDecodeAudio() takes into account the amount of decoded audio
  // that's been written to the AudioStream but not played yet. So if we
  // were calling NeedToDecodeAudio() twice and we thread-context switch
  // between the calls, audio can play, which can affect the return value
  // of NeedToDecodeAudio() giving inconsistent results. So we cache the
  // value returned by NeedToDecodeAudio(), and make decisions
  // based on the cached value. If NeedToDecodeAudio() has
  // returned false, and then subsequently returns true and we're not
  // playing, it will probably be OK since we don't need to consume data
  // anyway.

  const bool needToDecodeAudio = NeedToDecodeAudio();
  const bool needToDecodeVideo = NeedToDecodeVideo();

  // If we're in completed state, we should not need to decode anything else.
  MOZ_ASSERT(mState != DECODER_STATE_COMPLETED ||
             (!needToDecodeAudio && !needToDecodeVideo));

  bool needIdle = mDecoder->GetState() == MediaDecoder::PLAY_STATE_PAUSED &&
                  !needToDecodeAudio &&
                  !needToDecodeVideo &&
                  !IsPlaying();

  if (needToDecodeAudio) {
    EnsureAudioDecodeTaskQueued();
  }
  if (needToDecodeVideo) {
    EnsureVideoDecodeTaskQueued();
  }

  if (mIsReaderIdle == needIdle) {
    return;
  }
  mIsReaderIdle = needIdle;
  nsRefPtr<nsIRunnable> event;
  if (mIsReaderIdle) {
    event = NS_NewRunnableMethod(this, &MediaDecoderStateMachine::SetReaderIdle);
  } else {
    event = NS_NewRunnableMethod(this, &MediaDecoderStateMachine::SetReaderActive);
  }
  if (NS_FAILED(mDecodeTaskQueue->Dispatch(event)) &&
      mState != DECODER_STATE_SHUTDOWN) {
    NS_WARNING("Failed to dispatch event to set decoder idle state");
  }
}

nsresult
MediaDecoderStateMachine::EnqueueDecodeSeekTask()
{
  NS_ASSERTION(OnStateMachineThread() || OnDecodeThread(),
               "Should be on state machine or decode thread.");
  AssertCurrentThreadInMonitor();

  if (mState != DECODER_STATE_SEEKING) {
    return NS_OK;
  }
  nsresult rv = mDecodeTaskQueue->Dispatch(
    NS_NewRunnableMethod(this, &MediaDecoderStateMachine::DecodeSeek));
  NS_ENSURE_SUCCESS(rv, rv);

  return NS_OK;
}

nsresult
MediaDecoderStateMachine::DispatchAudioDecodeTaskIfNeeded()
{
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  NS_ASSERTION(OnStateMachineThread() || OnDecodeThread(),
               "Should be on state machine or decode thread.");

  if (NeedToDecodeAudio()) {
    return EnsureAudioDecodeTaskQueued();
  }

  return NS_OK;
}

nsresult
MediaDecoderStateMachine::EnsureAudioDecodeTaskQueued()
{
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  NS_ASSERTION(OnStateMachineThread() || OnDecodeThread(),
               "Should be on state machine or decode thread.");

  if (mState >= DECODER_STATE_COMPLETED) {
    return NS_OK;
  }

  MOZ_ASSERT(mState > DECODER_STATE_DECODING_METADATA);

  if (mIsAudioDecoding && !mDispatchedAudioDecodeTask) {
    nsresult rv = mDecodeTaskQueue->Dispatch(
      NS_NewRunnableMethod(this, &MediaDecoderStateMachine::DecodeAudio));
    if (NS_SUCCEEDED(rv)) {
      mDispatchedAudioDecodeTask = true;
    } else {
      NS_WARNING("Failed to dispatch task to decode audio");
    }
  }

  return NS_OK;
}

nsresult
MediaDecoderStateMachine::DispatchVideoDecodeTaskIfNeeded()
{
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  NS_ASSERTION(OnStateMachineThread() || OnDecodeThread(),
               "Should be on state machine or decode thread.");

  if (NeedToDecodeVideo()) {
    return EnsureVideoDecodeTaskQueued();
  }

  return NS_OK;
}

nsresult
MediaDecoderStateMachine::EnsureVideoDecodeTaskQueued()
{
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  NS_ASSERTION(OnStateMachineThread() || OnDecodeThread(),
               "Should be on state machine or decode thread.");

  if (mState >= DECODER_STATE_COMPLETED) {
    return NS_OK;
  }

  MOZ_ASSERT(mState > DECODER_STATE_DECODING_METADATA);

  if (mIsVideoDecoding && !mDispatchedVideoDecodeTask) {
    nsresult rv = mDecodeTaskQueue->Dispatch(
      NS_NewRunnableMethod(this, &MediaDecoderStateMachine::DecodeVideo));
    if (NS_SUCCEEDED(rv)) {
      mDispatchedVideoDecodeTask = true;
    } else {
      NS_WARNING("Failed to dispatch task to decode video");
    }
  }

  return NS_OK;
}

nsresult
MediaDecoderStateMachine::StartAudioThread()
{
  NS_ASSERTION(OnStateMachineThread() || OnDecodeThread(),
               "Should be on state machine or decode thread.");
  AssertCurrentThreadInMonitor();
  if (mAudioCaptured) {
    NS_ASSERTION(mStopAudioThread, "mStopAudioThread must always be true if audio is captured");
    return NS_OK;
  }

  mStopAudioThread = false;
  if (HasAudio() && !mAudioThread) {
    nsresult rv = NS_NewNamedThread("Media Audio",
                                    getter_AddRefs(mAudioThread),
                                    nullptr,
                                    MEDIA_THREAD_STACK_SIZE);
    if (NS_FAILED(rv)) {
      DECODER_LOG(PR_LOG_DEBUG, ("%p Changed state to SHUTDOWN because failed to create audio thread", mDecoder.get()));
      mState = DECODER_STATE_SHUTDOWN;
      return rv;
    }

    nsCOMPtr<nsIRunnable> event =
      NS_NewRunnableMethod(this, &MediaDecoderStateMachine::AudioLoop);
    mAudioThread->Dispatch(event, NS_DISPATCH_NORMAL);
  }
  return NS_OK;
}

int64_t MediaDecoderStateMachine::AudioDecodedUsecs() const
{
  NS_ASSERTION(HasAudio(),
               "Should only call AudioDecodedUsecs() when we have audio");
  // The amount of audio we have decoded is the amount of audio data we've
  // already decoded and pushed to the hardware, plus the amount of audio
  // data waiting to be pushed to the hardware.
  int64_t pushed = (mAudioEndTime != -1) ? (mAudioEndTime - GetMediaTime()) : 0;
  return pushed + mReader->AudioQueue().Duration();
}

bool MediaDecoderStateMachine::HasLowDecodedData(int64_t aAudioUsecs) const
{
  AssertCurrentThreadInMonitor();
  // We consider ourselves low on decoded data if we're low on audio,
  // provided we've not decoded to the end of the audio stream, or
  // if we're low on video frames, provided
  // we've not decoded to the end of the video stream.
  return ((HasAudio() &&
           !mReader->AudioQueue().IsFinished() &&
           AudioDecodedUsecs() < aAudioUsecs)
          ||
         (HasVideo() &&
          !mReader->VideoQueue().IsFinished() &&
          static_cast<uint32_t>(mReader->VideoQueue().GetSize()) < LOW_VIDEO_FRAMES));
}

bool MediaDecoderStateMachine::HasLowUndecodedData() const
{
  return HasLowUndecodedData(mLowDataThresholdUsecs);
}

bool MediaDecoderStateMachine::HasLowUndecodedData(double aUsecs) const
{
  AssertCurrentThreadInMonitor();
  NS_ASSERTION(mState > DECODER_STATE_DECODING_METADATA,
               "Must have loaded metadata for GetBuffered() to work");

  bool reliable;
  double bytesPerSecond = mDecoder->ComputePlaybackRate(&reliable);
  if (!reliable) {
    // Default to assuming we have enough
    return false;
  }

  MediaResource* stream = mDecoder->GetResource();
  int64_t currentPos = stream->Tell();
  int64_t requiredPos = currentPos + int64_t((aUsecs/1000000.0)*bytesPerSecond);
  int64_t length = stream->GetLength();
  if (length >= 0) {
    requiredPos = std::min(requiredPos, length);
  }

  return stream->GetCachedDataEnd(currentPos) < requiredPos;
}

void MediaDecoderStateMachine::SetFrameBufferLength(uint32_t aLength)
{
  NS_ASSERTION(aLength >= 512 && aLength <= 16384,
               "The length must be between 512 and 16384");
  AssertCurrentThreadInMonitor();
  mEventManager.SetSignalBufferLength(aLength);
}

void
MediaDecoderStateMachine::DecodeError()
{
  AssertCurrentThreadInMonitor();
  NS_ASSERTION(OnDecodeThread(), "Should be on decode thread.");

  // Change state to shutdown before sending error report to MediaDecoder
  // and the HTMLMediaElement, so that our pipeline can start exiting
  // cleanly during the sync dispatch below.
  DECODER_LOG(PR_LOG_DEBUG, ("%p Changed state to SHUTDOWN", mDecoder.get()));
  ScheduleStateMachine();
  mState = DECODER_STATE_SHUTDOWN;
  mDecoder->GetReentrantMonitor().NotifyAll();

  // Dispatch the event to call DecodeError synchronously. This ensures
  // we're in shutdown state by the time we exit the decode thread.
  // If we just moved to shutdown state here on the decode thread, we may
  // cause the state machine to shutdown/free memory without closing its
  // media stream properly, and we'll get callbacks from the media stream
  // causing a crash.
 {
    nsCOMPtr<nsIRunnable> event =
      NS_NewRunnableMethod(mDecoder, &MediaDecoder::DecodeError);
    ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
    NS_DispatchToMainThread(event, NS_DISPATCH_SYNC);
  }
}

void
MediaDecoderStateMachine::CallDecodeMetadata()
{
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  if (mState != DECODER_STATE_DECODING_METADATA) {
    return;
  }
  if (NS_FAILED(DecodeMetadata())) {
    DECODER_LOG(PR_LOG_DEBUG, ("Decode metadata failed, shutting down decoder"));
    DecodeError();
  }
}

nsresult MediaDecoderStateMachine::DecodeMetadata()
{
  AssertCurrentThreadInMonitor();
  NS_ASSERTION(OnDecodeThread(), "Should be on decode thread.");
  DECODER_LOG(PR_LOG_DEBUG, ("%p Decoding Media Headers", mDecoder.get()));
  if (mState != DECODER_STATE_DECODING_METADATA) {
    return NS_ERROR_FAILURE;
  }
  EnsureActive();

  nsresult res;
  MediaInfo info;
  MetadataTags* tags;
  {
    ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
    res = mReader->ReadMetadata(&info, &tags);
  }
  if (NS_SUCCEEDED(res) &&
      mState == DECODER_STATE_DECODING_METADATA &&
      mReader->IsWaitingMediaResources()) {
    // change state to DECODER_STATE_WAIT_FOR_RESOURCES
    StartWaitForResources();
    return NS_OK;
  }

  mInfo = info;

  if (NS_FAILED(res) || (!info.HasValidMedia())) {
    return NS_ERROR_FAILURE;
  }
  mDecoder->StartProgressUpdates();
  mGotDurationFromMetaData = (GetDuration() != -1);

  VideoData* videoData = FindStartTime();
  if (videoData) {
    ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
    RenderVideoFrame(videoData, TimeStamp::Now());
  }

  if (mState == DECODER_STATE_SHUTDOWN) {
    return NS_ERROR_FAILURE;
  }

  NS_ASSERTION(mStartTime != -1, "Must have start time");
  MOZ_ASSERT((!HasVideo() && !HasAudio()) ||
              !(mMediaSeekable && mTransportSeekable) || mEndTime != -1,
              "Active seekable media should have end time");
  MOZ_ASSERT(!(mMediaSeekable && mTransportSeekable) ||
             GetDuration() != -1, "Seekable media should have duration");
  DECODER_LOG(PR_LOG_DEBUG, ("%p Media goes from %lld to %lld (duration %lld)"
                             " transportSeekable=%d, mediaSeekable=%d",
                             mDecoder.get(), mStartTime, mEndTime, GetDuration(),
                             mTransportSeekable, mMediaSeekable));

  if (HasAudio() && !HasVideo()) {
    // We're playing audio only. We don't need to worry about slow video
    // decodes causing audio underruns, so don't buffer so much audio in
    // order to reduce memory usage.
    mAmpleAudioThresholdUsecs /= NO_VIDEO_AMPLE_AUDIO_DIVISOR;
    mLowAudioThresholdUsecs /= NO_VIDEO_AMPLE_AUDIO_DIVISOR;
  }

  // Inform the element that we've loaded the metadata and the first frame,
  // setting the default framebuffer size for audioavailable events.  Also,
  // if there is audio, let the MozAudioAvailable event manager know about
  // the metadata.
  if (HasAudio()) {
    mEventManager.Init(mInfo.mAudio.mChannels, mInfo.mAudio.mRate);
    // Set the buffer length at the decoder level to be able, to be able
    // to retrive the value via media element method. The RequestFrameBufferLength
    // will call the MediaDecoderStateMachine::SetFrameBufferLength().
    uint32_t frameBufferLength = mInfo.mAudio.mChannels * FRAMEBUFFER_LENGTH_PER_CHANNEL;
    mDecoder->RequestFrameBufferLength(frameBufferLength);
  }

  nsCOMPtr<nsIRunnable> metadataLoadedEvent =
    new AudioMetadataEventRunner(mDecoder,
                                 mInfo.mAudio.mChannels,
                                 mInfo.mAudio.mRate,
                                 HasAudio(),
                                 HasVideo(),
                                 tags);
  NS_DispatchToMainThread(metadataLoadedEvent, NS_DISPATCH_NORMAL);

  if (HasAudio()) {
    RefPtr<nsIRunnable> decodeTask(
      NS_NewRunnableMethod(this, &MediaDecoderStateMachine::DispatchAudioDecodeTaskIfNeeded));
    mReader->AudioQueue().AddPopListener(decodeTask, mDecodeTaskQueue);
  }
  if (HasVideo()) {
    RefPtr<nsIRunnable> decodeTask(
      NS_NewRunnableMethod(this, &MediaDecoderStateMachine::DispatchVideoDecodeTaskIfNeeded));
    mReader->VideoQueue().AddPopListener(decodeTask, mDecodeTaskQueue);
  }

  if (mState == DECODER_STATE_DECODING_METADATA) {
    DECODER_LOG(PR_LOG_DEBUG, ("%p Changed state from DECODING_METADATA to DECODING", mDecoder.get()));
    StartDecoding();
  }

  // For very short media FindStartTime() can decode the entire media.
  // So we need to check if this has occurred, else our decode pipeline won't
  // run (since it doesn't need to) and we won't detect end of stream.
  CheckIfDecodeComplete();

  if ((mState == DECODER_STATE_DECODING || mState == DECODER_STATE_COMPLETED) &&
      mDecoder->GetState() == MediaDecoder::PLAY_STATE_PLAYING &&
      !IsPlaying())
  {
    StartPlayback();
  }

  return NS_OK;
}

void MediaDecoderStateMachine::DecodeSeek()
{
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  NS_ASSERTION(OnDecodeThread(), "Should be on decode thread.");
  if (mState != DECODER_STATE_SEEKING) {
    return;
  }
  EnsureActive();

  // During the seek, don't have a lock on the decoder state,
  // otherwise long seek operations can block the main thread.
  // The events dispatched to the main thread are SYNC calls.
  // These calls are made outside of the decode monitor lock so
  // it is safe for the main thread to makes calls that acquire
  // the lock since it won't deadlock. We check the state when
  // acquiring the lock again in case shutdown has occurred
  // during the time when we didn't have the lock.
  int64_t seekTime = mSeekTime;
  mDecoder->StopProgressUpdates();

  bool currentTimeChanged = false;
  int64_t mediaTime = GetMediaTime();
  if (mediaTime != seekTime) {
    currentTimeChanged = true;
    // Stop playback now to ensure that while we're outside the monitor
    // dispatching SeekingStarted, playback doesn't advance and mess with
    // mCurrentFrameTime that we've setting to seekTime here.
    StopPlayback();
    UpdatePlaybackPositionInternal(seekTime);
  }

  // SeekingStarted will do a UpdateReadyStateForData which will
  // inform the element and its users that we have no frames
  // to display
  {
    ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
    nsCOMPtr<nsIRunnable> startEvent =
      NS_NewRunnableMethod(mDecoder, &MediaDecoder::SeekingStarted);
    NS_DispatchToMainThread(startEvent, NS_DISPATCH_SYNC);
  }

  if (currentTimeChanged) {
    // The seek target is different than the current playback position,
    // we'll need to seek the playback position, so shutdown our decode
    // and audio threads.
    StopAudioThread();
    ResetPlayback();
    nsresult res;
    {
      ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
      // Now perform the seek. We must not hold the state machine monitor
      // while we seek, since the seek reads, which could block on I/O.
      res = mReader->Seek(seekTime,
                          mStartTime,
                          mEndTime,
                          mediaTime);
    }
    if (NS_SUCCEEDED(res)) {
      AudioData* audio = HasAudio() ? mReader->AudioQueue().PeekFront() : nullptr;
      MOZ_ASSERT(!audio ||
                 (audio->mTime <= seekTime &&
                  seekTime <= audio->mTime + audio->mDuration) ||
                 mReader->AudioQueue().IsFinished(),
                 "Seek target should lie inside the first audio block after seek");
      int64_t startTime = (audio && audio->mTime < seekTime) ? audio->mTime : seekTime;
      mAudioStartTime = startTime;
      mPlayDuration = startTime - mStartTime;
      if (HasVideo()) {
        VideoData* video = mReader->VideoQueue().PeekFront();
        if (video) {
          MOZ_ASSERT((video->mTime <= seekTime && seekTime <= video->GetEndTime()) ||
                     mReader->VideoQueue().IsFinished(),
            "Seek target should lie inside the first frame after seek, unless it's the last frame.");
          {
            ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
            RenderVideoFrame(video, TimeStamp::Now());
          }
          nsCOMPtr<nsIRunnable> event =
            NS_NewRunnableMethod(mDecoder, &MediaDecoder::Invalidate);
          NS_DispatchToMainThread(event, NS_DISPATCH_NORMAL);
        }
      }
    } else {
      DecodeError();
    }
  }
  mDecoder->StartProgressUpdates();
  if (mState == DECODER_STATE_DECODING_METADATA ||
      mState == DECODER_STATE_DORMANT ||
      mState == DECODER_STATE_SHUTDOWN) {
    return;
  }

  // Try to decode another frame to detect if we're at the end...
  DECODER_LOG(PR_LOG_DEBUG, ("%p Seek completed, mCurrentFrameTime=%lld\n",
              mDecoder.get(), mCurrentFrameTime));

  // Change state to DECODING or COMPLETED now. SeekingStopped will
  // call MediaDecoderStateMachine::Seek to reset our state to SEEKING
  // if we need to seek again.

  nsCOMPtr<nsIRunnable> stopEvent;
  bool isLiveStream = mDecoder->GetResource()->GetLength() == -1;
  if (GetMediaTime() == mEndTime && !isLiveStream) {
    // Seeked to end of media, move to COMPLETED state. Note we don't do
    // this if we're playing a live stream, since the end of media will advance
    // once we download more data!
    DECODER_LOG(PR_LOG_DEBUG, ("%p Changed state from SEEKING (to %lld) to COMPLETED",
                               mDecoder.get(), seekTime));
    stopEvent = NS_NewRunnableMethod(mDecoder, &MediaDecoder::SeekingStoppedAtEnd);
    // Explicitly set our state so we don't decode further, and so
    // we report playback ended to the media element.
    mState = DECODER_STATE_COMPLETED;
    mIsAudioDecoding = false;
    mIsVideoDecoding = false;
    DispatchDecodeTasksIfNeeded();
  } else {
    DECODER_LOG(PR_LOG_DEBUG, ("%p Changed state from SEEKING (to %lld) to DECODING",
                               mDecoder.get(), seekTime));
    stopEvent = NS_NewRunnableMethod(mDecoder, &MediaDecoder::SeekingStopped);
    StartDecoding();
  }
  {
    ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
    NS_DispatchToMainThread(stopEvent, NS_DISPATCH_SYNC);
  }

  // Reset quick buffering status. This ensures that if we began the
  // seek while quick-buffering, we won't bypass quick buffering mode
  // if we need to buffer after the seek.
  mQuickBuffering = false;

  ScheduleStateMachine();
}

// Runnable to dispose of the decoder and state machine on the main thread.
class nsDecoderDisposeEvent : public nsRunnable {
public:
  nsDecoderDisposeEvent(already_AddRefed<MediaDecoder> aDecoder,
                        already_AddRefed<MediaDecoderStateMachine> aStateMachine)
    : mDecoder(aDecoder), mStateMachine(aStateMachine) {}
  NS_IMETHOD Run() {
    NS_ASSERTION(NS_IsMainThread(), "Must be on main thread.");
    mStateMachine->ReleaseDecoder();
    mDecoder->ReleaseStateMachine();
    mStateMachine = nullptr;
    mDecoder = nullptr;
    return NS_OK;
  }
private:
  nsRefPtr<MediaDecoder> mDecoder;
  nsRefPtr<MediaDecoderStateMachine> mStateMachine;
};

// Runnable which dispatches an event to the main thread to dispose of the
// decoder and state machine. This runs on the state machine thread after
// the state machine has shutdown, and all events for that state machine have
// finished running.
class nsDispatchDisposeEvent : public nsRunnable {
public:
  nsDispatchDisposeEvent(MediaDecoder* aDecoder,
                         MediaDecoderStateMachine* aStateMachine)
    : mDecoder(aDecoder), mStateMachine(aStateMachine) {}
  NS_IMETHOD Run() {
    NS_DispatchToMainThread(new nsDecoderDisposeEvent(mDecoder.forget(),
                                                      mStateMachine.forget()));
    return NS_OK;
  }
private:
  nsRefPtr<MediaDecoder> mDecoder;
  nsRefPtr<MediaDecoderStateMachine> mStateMachine;
};

nsresult MediaDecoderStateMachine::RunStateMachine()
{
  AssertCurrentThreadInMonitor();

  MediaResource* resource = mDecoder->GetResource();
  NS_ENSURE_TRUE(resource, NS_ERROR_NULL_POINTER);

  switch (mState) {
    case DECODER_STATE_SHUTDOWN: {
      if (IsPlaying()) {
        StopPlayback();
      }
      StopAudioThread();
      // If mAudioThread is non-null after StopAudioThread completes, we are
      // running in a nested event loop waiting for Shutdown() on
      // mAudioThread to complete.  Return to the event loop and let it
      // finish processing before continuing with shutdown.
      if (mAudioThread) {
        MOZ_ASSERT(mStopAudioThread);
        return NS_OK;
      }

      // The reader's listeners hold references to the state machine,
      // creating a cycle which keeps the state machine and its shared
      // thread pools alive. So break it here.
      mReader->AudioQueue().ClearListeners();
      mReader->VideoQueue().ClearListeners();

      {
        ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
        // Wait for the thread decoding to exit.
        mDecodeTaskQueue->Shutdown();
        mReader->ReleaseMediaResources();
      }
      // Now that those threads are stopped, there's no possibility of
      // mPendingWakeDecoder being needed again. Revoke it.
      mPendingWakeDecoder = nullptr;

      MOZ_ASSERT(mState == DECODER_STATE_SHUTDOWN,
                 "How did we escape from the shutdown state?");
      // We must daisy-chain these events to destroy the decoder. We must
      // destroy the decoder on the main thread, but we can't destroy the
      // decoder while this thread holds the decoder monitor. We can't
      // dispatch an event to the main thread to destroy the decoder from
      // here, as the event may run before the dispatch returns, and we
      // hold the decoder monitor here. We also want to guarantee that the
      // state machine is destroyed on the main thread, and so the
      // event runner running this function (which holds a reference to the
      // state machine) needs to finish and be released in order to allow
      // that. So we dispatch an event to run after this event runner has
      // finished and released its monitor/references. That event then will
      // dispatch an event to the main thread to release the decoder and
      // state machine.
      GetStateMachineThread()->Dispatch(
        new nsDispatchDisposeEvent(mDecoder, this), NS_DISPATCH_NORMAL);
      return NS_OK;
    }

    case DECODER_STATE_DORMANT: {
      if (IsPlaying()) {
        StopPlayback();
      }
      StopAudioThread();
      // Now that those threads are stopped, there's no possibility of
      // mPendingWakeDecoder being needed again. Revoke it.
      mPendingWakeDecoder = nullptr;
      {
        ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
        // Wait for the thread decoding, if any, to exit.
        mDecodeTaskQueue->AwaitIdle();
        mReader->ReleaseMediaResources();
      }
      return NS_OK;
    }

    case DECODER_STATE_WAIT_FOR_RESOURCES: {
      return NS_OK;
    }

    case DECODER_STATE_DECODING_METADATA: {
      // Ensure we have a decode thread to decode metadata.
      return EnqueueDecodeMetadataTask();
    }

    case DECODER_STATE_DECODING: {
      if (mDecoder->GetState() != MediaDecoder::PLAY_STATE_PLAYING &&
          IsPlaying())
      {
        // We're playing, but the element/decoder is in paused state. Stop
        // playing!
        StopPlayback();
      }

      if (mDecoder->GetState() == MediaDecoder::PLAY_STATE_PLAYING &&
          !IsPlaying()) {
        // We are playing, but the state machine does not know it yet. Tell it
        // that it is, so that the clock can be properly queried.
        StartPlayback();
      }

      AdvanceFrame();
      NS_ASSERTION(mDecoder->GetState() != MediaDecoder::PLAY_STATE_PLAYING ||
                   IsStateMachineScheduled() ||
                   mPlaybackRate == 0.0, "Must have timer scheduled");
      return NS_OK;
    }

    case DECODER_STATE_BUFFERING: {
      TimeStamp now = TimeStamp::Now();
      NS_ASSERTION(!mBufferingStart.IsNull(), "Must know buffering start time.");

      // We will remain in the buffering state if we've not decoded enough
      // data to begin playback, or if we've not downloaded a reasonable
      // amount of data inside our buffering time.
      TimeDuration elapsed = now - mBufferingStart;
      bool isLiveStream = resource->GetLength() == -1;
      if ((isLiveStream || !mDecoder->CanPlayThrough()) &&
            elapsed < TimeDuration::FromSeconds(mBufferingWait * mPlaybackRate) &&
            (mQuickBuffering ? HasLowDecodedData(QUICK_BUFFERING_LOW_DATA_USECS)
                            : HasLowUndecodedData(mBufferingWait * USECS_PER_S)) &&
            !mDecoder->IsDataCachedToEndOfResource() &&
            !resource->IsSuspended())
      {
        DECODER_LOG(PR_LOG_DEBUG,
                    ("%p Buffering: wait %ds, timeout in %.3lfs %s",
                      mDecoder.get(),
                      mBufferingWait,
                      mBufferingWait - elapsed.ToSeconds(),
                      (mQuickBuffering ? "(quick exit)" : "")));
        ScheduleStateMachine(USECS_PER_S);
        return NS_OK;
      } else {
        DECODER_LOG(PR_LOG_DEBUG, ("%p Changed state from BUFFERING to DECODING", mDecoder.get()));
        DECODER_LOG(PR_LOG_DEBUG, ("%p Buffered for %.3lfs",
                                   mDecoder.get(),
                                   (now - mBufferingStart).ToSeconds()));
        StartDecoding();
      }

      // Notify to allow blocked decoder thread to continue
      mDecoder->GetReentrantMonitor().NotifyAll();
      UpdateReadyState();
      if (mDecoder->GetState() == MediaDecoder::PLAY_STATE_PLAYING &&
          !IsPlaying())
      {
        StartPlayback();
      }
      NS_ASSERTION(IsStateMachineScheduled(), "Must have timer scheduled");
      return NS_OK;
    }

    case DECODER_STATE_SEEKING: {
      // Ensure we have a decode thread to perform the seek.
     return EnqueueDecodeSeekTask();
    }

    case DECODER_STATE_COMPLETED: {
      // Play the remaining media. We want to run AdvanceFrame() at least
      // once to ensure the current playback position is advanced to the
      // end of the media, and so that we update the readyState.
      if (mReader->VideoQueue().GetSize() > 0 ||
          (HasAudio() && !mAudioCompleted) ||
          (mDecoder->GetDecodedStream() && !mDecoder->GetDecodedStream()->IsFinished()))
      {
        AdvanceFrame();
        NS_ASSERTION(mDecoder->GetState() != MediaDecoder::PLAY_STATE_PLAYING ||
                     mPlaybackRate == 0 ||
                     IsStateMachineScheduled(),
                     "Must have timer scheduled");
        return NS_OK;
      }

      // StopPlayback in order to reset the IsPlaying() state so audio
      // is restarted correctly.
      StopPlayback();

      if (mState != DECODER_STATE_COMPLETED) {
        // While we're presenting a frame we can change state. Whatever changed
        // our state should have scheduled another state machine run.
        NS_ASSERTION(IsStateMachineScheduled(), "Must have timer scheduled");
        return NS_OK;
      }

      StopAudioThread();
      // When we're decoding to a stream, the stream's main-thread finish signal
      // will take care of calling MediaDecoder::PlaybackEnded.
      if (mDecoder->GetState() == MediaDecoder::PLAY_STATE_PLAYING &&
          !mDecoder->GetDecodedStream()) {
        int64_t videoTime = HasVideo() ? mVideoFrameEndTime : 0;
        int64_t clockTime = std::max(mEndTime, std::max(videoTime, GetAudioClock()));
        UpdatePlaybackPosition(clockTime);

        {
          // Wait for the state change is completed in the main thread,
          // otherwise we might see |mDecoder->GetState() == MediaDecoder::PLAY_STATE_PLAYING|
          // in next loop and send |MediaDecoder::PlaybackEnded| again to trigger 'ended'
          // event twice in the media element.
          ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
          nsCOMPtr<nsIRunnable> event =
            NS_NewRunnableMethod(mDecoder, &MediaDecoder::PlaybackEnded);
          NS_DispatchToMainThread(event, NS_DISPATCH_SYNC);
        }
      }
      return NS_OK;
    }
  }

  return NS_OK;
}

void MediaDecoderStateMachine::RenderVideoFrame(VideoData* aData,
                                                TimeStamp aTarget)
{
  NS_ASSERTION(OnStateMachineThread() || OnDecodeThread(),
               "Should be on state machine or decode thread.");
  mDecoder->GetReentrantMonitor().AssertNotCurrentThreadIn();

  if (aData->mDuplicate) {
    return;
  }

  if (!PR_GetEnv("MOZ_QUIET")) {
    DECODER_LOG(PR_LOG_DEBUG, ("%p Decoder playing video frame %lld",
                               mDecoder.get(), aData->mTime));
  }

  VideoFrameContainer* container = mDecoder->GetVideoFrameContainer();
  if (container) {
    container->SetCurrentFrame(ThebesIntSize(aData->mDisplay), aData->mImage,
                               aTarget);
  }
}

int64_t
MediaDecoderStateMachine::GetAudioClock()
{
  // We must hold the decoder monitor while using the audio stream off the
  // audio thread to ensure that it doesn't get destroyed on the audio thread
  // while we're using it.
  AssertCurrentThreadInMonitor();
  if (!HasAudio() || mAudioCaptured)
    return -1;
  if (!mAudioStream) {
    // Audio thread hasn't played any data yet.
    return mAudioStartTime;
  }
  int64_t t = mAudioStream->GetPosition();
  return (t == -1) ? -1 : t + mAudioStartTime;
}

int64_t MediaDecoderStateMachine::GetVideoStreamPosition()
{
  AssertCurrentThreadInMonitor();

  if (!IsPlaying()) {
    return mPlayDuration + mStartTime;
  }

  // The playbackRate has been just been changed, reset the playstartTime.
  if (mResetPlayStartTime) {
    mPlayStartTime = TimeStamp::Now();
    mResetPlayStartTime = false;
  }

  int64_t pos = DurationToUsecs(TimeStamp::Now() - mPlayStartTime) + mPlayDuration;
  pos -= mBasePosition;
  NS_ASSERTION(pos >= 0, "Video stream position should be positive.");
  return mBasePosition + pos * mPlaybackRate + mStartTime;
}

int64_t MediaDecoderStateMachine::GetClock()
{
  AssertCurrentThreadInMonitor();

  // Determine the clock time. If we've got audio, and we've not reached
  // the end of the audio, use the audio clock. However if we've finished
  // audio, or don't have audio, use the system clock. If our output is being
  // fed to a MediaStream, use that stream as the source of the clock.
  int64_t clock_time = -1;
  DecodedStreamData* stream = mDecoder->GetDecodedStream();
  if (!IsPlaying()) {
    clock_time = mPlayDuration + mStartTime;
  } else if (stream) {
    clock_time = GetCurrentTimeViaMediaStreamSync();
  } else {
    int64_t audio_time = GetAudioClock();
    if (HasAudio() && !mAudioCompleted && audio_time != -1) {
      clock_time = audio_time;
      // Resync against the audio clock, while we're trusting the
      // audio clock. This ensures no "drift", particularly on Linux.
      mPlayDuration = clock_time - mStartTime;
      mPlayStartTime = TimeStamp::Now();
    } else {
      // Audio is disabled on this system. Sync to the system clock.
      clock_time = GetVideoStreamPosition();
      // Ensure the clock can never go backwards.
      NS_ASSERTION(mCurrentFrameTime <= clock_time || mPlaybackRate <= 0,
          "Clock should go forwards if the playback rate is > 0.");
    }
  }
  return clock_time;
}

void MediaDecoderStateMachine::AdvanceFrame()
{
  NS_ASSERTION(OnStateMachineThread(), "Should be on state machine thread.");
  AssertCurrentThreadInMonitor();
  NS_ASSERTION(!HasAudio() || mAudioStartTime != -1,
               "Should know audio start time if we have audio.");

  if (mDecoder->GetState() != MediaDecoder::PLAY_STATE_PLAYING) {
    return;
  }

  // If playbackRate is 0.0, we should stop the progress, but not be in paused
  // state, per spec.
  if (mPlaybackRate == 0.0) {
    return;
  }

  int64_t clock_time = GetClock();
  // Skip frames up to the frame at the playback position, and figure out
  // the time remaining until it's time to display the next frame.
  int64_t remainingTime = AUDIO_DURATION_USECS;
  NS_ASSERTION(clock_time >= mStartTime, "Should have positive clock time.");
  nsAutoPtr<VideoData> currentFrame;
#ifdef PR_LOGGING
  int32_t droppedFrames = 0;
#endif
  if (mReader->VideoQueue().GetSize() > 0) {
    VideoData* frame = mReader->VideoQueue().PeekFront();
    while (mRealTime || clock_time >= frame->mTime) {
      mVideoFrameEndTime = frame->GetEndTime();
      currentFrame = frame;
#ifdef PR_LOGGING
      if (!PR_GetEnv("MOZ_QUIET")) {
        DECODER_LOG(PR_LOG_DEBUG, ("%p Decoder discarding video frame %lld", mDecoder.get(), frame->mTime));
        if (droppedFrames++) {
          DECODER_LOG(PR_LOG_DEBUG, ("%p Decoder discarding video frame %lld (%d so far)",
                      mDecoder.get(), frame->mTime, droppedFrames - 1));
        }
      }
#endif
      mReader->VideoQueue().PopFront();
      // Notify the decode thread that the video queue's buffers may have
      // free'd up space for more frames.
      mDecoder->GetReentrantMonitor().NotifyAll();
      mDecoder->UpdatePlaybackOffset(frame->mOffset);
      if (mReader->VideoQueue().GetSize() == 0)
        break;
      frame = mReader->VideoQueue().PeekFront();
    }
    // Current frame has already been presented, wait until it's time to
    // present the next frame.
    if (frame && !currentFrame) {
      int64_t now = IsPlaying() ? clock_time : mPlayDuration;

      remainingTime = frame->mTime - now;
    }
  }

  // Check to see if we don't have enough data to play up to the next frame.
  // If we don't, switch to buffering mode.
  MediaResource* resource = mDecoder->GetResource();
  if (mState == DECODER_STATE_DECODING &&
      mDecoder->GetState() == MediaDecoder::PLAY_STATE_PLAYING &&
      HasLowDecodedData(remainingTime + EXHAUSTED_DATA_MARGIN_USECS) &&
      !mDecoder->IsDataCachedToEndOfResource() &&
      !resource->IsSuspended()) {
    if (JustExitedQuickBuffering() || HasLowUndecodedData()) {
      if (currentFrame) {
        mReader->VideoQueue().PushFront(currentFrame.forget());
      }
      StartBuffering();
      ScheduleStateMachine();
      return;
    }
  }

  // We've got enough data to keep playing until at least the next frame.
  // Start playing now if need be.
  if (!IsPlaying() && ((mFragmentEndTime >= 0 && clock_time < mFragmentEndTime) || mFragmentEndTime < 0)) {
    StartPlayback();
  }

  if (currentFrame) {
    // Decode one frame and display it.
    TimeStamp presTime = mPlayStartTime - UsecsToDuration(mPlayDuration) +
                          UsecsToDuration(currentFrame->mTime - mStartTime);
    NS_ASSERTION(currentFrame->mTime >= mStartTime, "Should have positive frame time");
    {
      ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
      // If we have video, we want to increment the clock in steps of the frame
      // duration.
      RenderVideoFrame(currentFrame, presTime);
    }
    // If we're no longer playing after dropping and reacquiring the lock,
    // playback must've been stopped on the decode thread (by a seek, for
    // example).  In that case, the current frame is probably out of date.
    if (!IsPlaying()) {
      ScheduleStateMachine();
      return;
    }
    MediaDecoder::FrameStatistics& frameStats = mDecoder->GetFrameStatistics();
    frameStats.NotifyPresentedFrame();
    remainingTime = currentFrame->GetEndTime() - clock_time;
    currentFrame = nullptr;
  }

  // Cap the current time to the larger of the audio and video end time.
  // This ensures that if we're running off the system clock, we don't
  // advance the clock to after the media end time.
  if (mVideoFrameEndTime != -1 || mAudioEndTime != -1) {
    // These will be non -1 if we've displayed a video frame, or played an audio frame.
    clock_time = std::min(clock_time, std::max(mVideoFrameEndTime, mAudioEndTime));
    if (clock_time > GetMediaTime()) {
      // Only update the playback position if the clock time is greater
      // than the previous playback position. The audio clock can
      // sometimes report a time less than its previously reported in
      // some situations, and we need to gracefully handle that.
      UpdatePlaybackPosition(clock_time);
    }
  }

  // If the number of audio/video frames queued has changed, either by
  // this function popping and playing a video frame, or by the audio
  // thread popping and playing an audio frame, we may need to update our
  // ready state. Post an update to do so.
  UpdateReadyState();

  ScheduleStateMachine(remainingTime);
}

void MediaDecoderStateMachine::Wait(int64_t aUsecs) {
  NS_ASSERTION(OnAudioThread(), "Only call on the audio thread");
  AssertCurrentThreadInMonitor();
  TimeStamp end = TimeStamp::Now() + UsecsToDuration(std::max<int64_t>(USECS_PER_MS, aUsecs));
  TimeStamp now;
  while ((now = TimeStamp::Now()) < end &&
         mState != DECODER_STATE_SHUTDOWN &&
         mState != DECODER_STATE_SEEKING &&
         !mStopAudioThread &&
         IsPlaying())
  {
    int64_t ms = static_cast<int64_t>(NS_round((end - now).ToSeconds() * 1000));
    if (ms == 0 || ms > UINT32_MAX) {
      break;
    }
    mDecoder->GetReentrantMonitor().Wait(PR_MillisecondsToInterval(static_cast<uint32_t>(ms)));
  }
}

VideoData* MediaDecoderStateMachine::FindStartTime()
{
  NS_ASSERTION(OnDecodeThread(), "Should be on decode thread.");
  AssertCurrentThreadInMonitor();
  int64_t startTime = 0;
  mStartTime = 0;
  VideoData* v = nullptr;
  {
    ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
    v = mReader->FindStartTime(startTime);
  }
  if (startTime != 0) {
    mStartTime = startTime;
    if (mGotDurationFromMetaData) {
      NS_ASSERTION(mEndTime != -1,
                   "We should have mEndTime as supplied duration here");
      // We were specified a duration from a Content-Duration HTTP header.
      // Adjust mEndTime so that mEndTime-mStartTime matches the specified
      // duration.
      mEndTime = mStartTime + mEndTime;
    }
  }
  // Set the audio start time to be start of media. If this lies before the
  // first actual audio frame we have, we'll inject silence during playback
  // to ensure the audio starts at the correct time.
  mAudioStartTime = mStartTime;
  DECODER_LOG(PR_LOG_DEBUG, ("%p Media start time is %lld", mDecoder.get(), mStartTime));
  return v;
}

void MediaDecoderStateMachine::UpdateReadyState() {
  AssertCurrentThreadInMonitor();

  MediaDecoderOwner::NextFrameStatus nextFrameStatus = GetNextFrameStatus();
  if (nextFrameStatus == mLastFrameStatus) {
    return;
  }
  mLastFrameStatus = nextFrameStatus;

  /* This is a bit tricky. MediaDecoder::UpdateReadyStateForData will run on
   * the main thread and re-evaluate GetNextFrameStatus there, passing it to
   * HTMLMediaElement::UpdateReadyStateForData. It doesn't use the value of
   * GetNextFrameStatus we computed here, because what we're computing here
   * could be stale by the time MediaDecoder::UpdateReadyStateForData runs.
   * We only compute GetNextFrameStatus here to avoid posting runnables to the main
   * thread unnecessarily.
   */
  nsCOMPtr<nsIRunnable> event;
  event = NS_NewRunnableMethod(mDecoder, &MediaDecoder::UpdateReadyStateForData);
  NS_DispatchToMainThread(event, NS_DISPATCH_NORMAL);
}

bool MediaDecoderStateMachine::JustExitedQuickBuffering()
{
  return !mDecodeStartTime.IsNull() &&
    mQuickBuffering &&
    (TimeStamp::Now() - mDecodeStartTime) < TimeDuration::FromMicroseconds(QUICK_BUFFER_THRESHOLD_USECS);
}

void MediaDecoderStateMachine::StartBuffering()
{
  AssertCurrentThreadInMonitor();

  if (mState != DECODER_STATE_DECODING) {
    // We only move into BUFFERING state if we're actually decoding.
    // If we're currently doing something else, we don't need to buffer,
    // and more importantly, we shouldn't overwrite mState to interrupt
    // the current operation, as that could leave us in an inconsistent
    // state!
    return;
  }

  if (IsPlaying()) {
    StopPlayback();
  }

  TimeDuration decodeDuration = TimeStamp::Now() - mDecodeStartTime;
  // Go into quick buffering mode provided we've not just left buffering using
  // a "quick exit". This stops us flip-flopping between playing and buffering
  // when the download speed is similar to the decode speed.
  mQuickBuffering =
    !JustExitedQuickBuffering() &&
    decodeDuration < UsecsToDuration(QUICK_BUFFER_THRESHOLD_USECS);
  mBufferingStart = TimeStamp::Now();

  // We need to tell the element that buffering has started.
  // We can't just directly send an asynchronous runnable that
  // eventually fires the "waiting" event. The problem is that
  // there might be pending main-thread events, such as "data
  // received" notifications, that mean we're not actually still
  // buffering by the time this runnable executes. So instead
  // we just trigger UpdateReadyStateForData; when it runs, it
  // will check the current state and decide whether to tell
  // the element we're buffering or not.
  UpdateReadyState();
  mState = DECODER_STATE_BUFFERING;
  DECODER_LOG(PR_LOG_DEBUG, ("%p Changed state from DECODING to BUFFERING, decoded for %.3lfs",
                             mDecoder.get(), decodeDuration.ToSeconds()));
#ifdef PR_LOGGING
  MediaDecoder::Statistics stats = mDecoder->GetStatistics();
  DECODER_LOG(PR_LOG_DEBUG, ("%p Playback rate: %.1lfKB/s%s download rate: %.1lfKB/s%s",
              mDecoder.get(),
              stats.mPlaybackRate/1024, stats.mPlaybackRateReliable ? "" : " (unreliable)",
              stats.mDownloadRate/1024, stats.mDownloadRateReliable ? "" : " (unreliable)"));
#endif
}

nsresult MediaDecoderStateMachine::GetBuffered(dom::TimeRanges* aBuffered) {
  MediaResource* resource = mDecoder->GetResource();
  NS_ENSURE_TRUE(resource, NS_ERROR_FAILURE);
  resource->Pin();
  nsresult res = mReader->GetBuffered(aBuffered, mStartTime);
  resource->Unpin();
  return res;
}

nsresult MediaDecoderStateMachine::Run()
{
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  NS_ASSERTION(OnStateMachineThread(), "Should be on state machine thread.");

  return CallRunStateMachine();
}

nsresult MediaDecoderStateMachine::CallRunStateMachine()
{
  AssertCurrentThreadInMonitor();
  NS_ASSERTION(OnStateMachineThread(), "Should be on state machine thread.");
  // This will be set to true by ScheduleStateMachine() if it's called
  // while we're in RunStateMachine().
  mRunAgain = false;

  // Set to true whenever we dispatch an event to run this state machine.
  // This flag prevents us from dispatching
  mDispatchedRunEvent = false;

  // If audio is being captured, stop the audio thread if it's running
  if (mAudioCaptured) {
    StopAudioThread();
  }

  mTimeout = TimeStamp();

  mIsRunning = true;
  nsresult res = RunStateMachine();
  mIsRunning = false;

  if (mRunAgain && !mDispatchedRunEvent) {
    mDispatchedRunEvent = true;
    return GetStateMachineThread()->Dispatch(this, NS_DISPATCH_NORMAL);
  }

  return res;
}

static void TimeoutExpired(nsITimer *aTimer, void *aClosure) {
  MediaDecoderStateMachine *machine =
    static_cast<MediaDecoderStateMachine*>(aClosure);
  NS_ASSERTION(machine, "Must have been passed state machine");
  machine->TimeoutExpired();
}

void MediaDecoderStateMachine::TimeoutExpired()
{
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  NS_ASSERTION(OnStateMachineThread(), "Must be on state machine thread");
  if (mIsRunning) {
    mRunAgain = true;
  } else if (!mDispatchedRunEvent) {
    // We don't have an event dispatched to run the state machine, so we
    // can just run it from here.
    CallRunStateMachine();
  }
  // Otherwise, an event has already been dispatched to run the state machine
  // as soon as possible. Nothing else needed to do, the state machine is
  // going to run anyway.
}

void MediaDecoderStateMachine::ScheduleStateMachineWithLockAndWakeDecoder() {
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
  DispatchAudioDecodeTaskIfNeeded();
  DispatchVideoDecodeTaskIfNeeded();
}

nsresult MediaDecoderStateMachine::ScheduleStateMachine(int64_t aUsecs) {
  AssertCurrentThreadInMonitor();
  NS_ABORT_IF_FALSE(GetStateMachineThread(),
    "Must have a state machine thread to schedule");

  if (mState == DECODER_STATE_SHUTDOWN) {
    return NS_ERROR_FAILURE;
  }
  aUsecs = std::max<int64_t>(aUsecs, 0);

  TimeStamp timeout = TimeStamp::Now() + UsecsToDuration(aUsecs);
  if (!mTimeout.IsNull()) {
    if (timeout >= mTimeout) {
      // We've already scheduled a timer set to expire at or before this time,
      // or have an event dispatched to run the state machine.
      return NS_OK;
    }
    if (mTimer) {
      // We've been asked to schedule a timer to run before an existing timer.
      // Cancel the existing timer.
      mTimer->Cancel();
    }
  }

  uint32_t ms = static_cast<uint32_t>((aUsecs / USECS_PER_MS) & 0xFFFFFFFF);
  if (mRealTime && ms > 40)
    ms = 40;
  if (ms == 0) {
    if (mIsRunning) {
      // We're currently running this state machine on the state machine
      // thread. Signal it to run again once it finishes its current cycle.
      mRunAgain = true;
      return NS_OK;
    } else if (!mDispatchedRunEvent) {
      // We're not currently running this state machine on the state machine
      // thread. Dispatch an event to run one cycle of the state machine.
      mDispatchedRunEvent = true;
      return GetStateMachineThread()->Dispatch(this, NS_DISPATCH_NORMAL);
    }
    // We're not currently running this state machine on the state machine
    // thread, but something has already dispatched an event to run it again,
    // so just exit; it's going to run real soon.
    return NS_OK;
  }

  // Since there is already a pending task that will run immediately,
  // we don't need to schedule a timer task.
  if (mRunAgain) {
    return NS_OK;
  }

  mTimeout = timeout;

  nsresult res;
  if (!mTimer) {
    mTimer = do_CreateInstance("@mozilla.org/timer;1", &res);
    if (NS_FAILED(res)) return res;
    mTimer->SetTarget(GetStateMachineThread());
  }

  res = mTimer->InitWithFuncCallback(mozilla::TimeoutExpired,
                                     this,
                                     ms,
                                     nsITimer::TYPE_ONE_SHOT);
  return res;
}

bool MediaDecoderStateMachine::OnDecodeThread() const
{
  return mDecodeTaskQueue->IsCurrentThreadIn();
}

bool MediaDecoderStateMachine::OnStateMachineThread() const
{
  bool rv = false;
  mStateMachineThreadPool->IsOnCurrentThread(&rv);
  return rv;
}

nsIEventTarget* MediaDecoderStateMachine::GetStateMachineThread()
{
  return mStateMachineThreadPool->GetEventTarget();
}

void MediaDecoderStateMachine::NotifyAudioAvailableListener()
{
  AssertCurrentThreadInMonitor();
  mEventManager.NotifyAudioAvailableListener();
}

void MediaDecoderStateMachine::SetPlaybackRate(double aPlaybackRate)
{
  NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");
  NS_ASSERTION(aPlaybackRate != 0,
      "PlaybackRate == 0 should be handled before this function.");
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());

  // We don't currently support more than two channels when changing playback
  // rate.
  if (mAudioStream && mAudioStream->GetChannels() > 2) {
    return;
  }

  if (mPlaybackRate == aPlaybackRate) {
    return;
  }

  // Get position of the last time we changed the rate.
  if (!HasAudio()) {
    // mBasePosition is a position in the video stream, not an absolute time.
    if (mState == DECODER_STATE_SEEKING) {
      mBasePosition = mSeekTime - mStartTime;
    } else {
      mBasePosition = GetVideoStreamPosition();
    }
    mPlayDuration = mBasePosition;
    mResetPlayStartTime = true;
    mPlayStartTime = TimeStamp::Now();
  }

  mPlaybackRate = aPlaybackRate;
}

void MediaDecoderStateMachine::SetPreservesPitch(bool aPreservesPitch)
{
  NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");
  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());

  mPreservesPitch = aPreservesPitch;

  return;
}

bool MediaDecoderStateMachine::IsShutdown()
{
  AssertCurrentThreadInMonitor();
  return GetState() == DECODER_STATE_SHUTDOWN;
}

void MediaDecoderStateMachine::QueueMetadata(int64_t aPublishTime,
                                             int aChannels,
                                             int aRate,
                                             bool aHasAudio,
                                             bool aHasVideo,
                                             MetadataTags* aTags)
{
  NS_ASSERTION(OnDecodeThread(), "Should be on decode thread.");
  AssertCurrentThreadInMonitor();
  TimedMetadata* metadata = new TimedMetadata;
  metadata->mPublishTime = aPublishTime;
  metadata->mChannels = aChannels;
  metadata->mRate = aRate;
  metadata->mHasAudio = aHasAudio;
  metadata->mHasVideo = aHasVideo;
  metadata->mTags = aTags;
  mMetadataManager.QueueMetadata(metadata);
}

} // namespace mozilla