gecko-dev/content/media/nsMediaDecoder.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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/. */

#include "nsMediaDecoder.h"
#include "MediaResource.h"

#include "nsHTMLMediaElement.h"
#include "nsDOMError.h"

using namespace mozilla;

// Number of milliseconds between progress events as defined by spec
static const PRUint32 PROGRESS_MS = 350;

// Number of milliseconds of no data before a stall event is fired as defined by spec
static const PRUint32 STALL_MS = 3000;

// Number of estimated seconds worth of data we need to have buffered 
// ahead of the current playback position before we allow the media decoder
// to report that it can play through the entire media without the decode
// catching up with the download. Having this margin make the
// nsMediaDecoder::CanPlayThrough() calculation more stable in the case of
// fluctuating bitrates.
static const PRInt64 CAN_PLAY_THROUGH_MARGIN = 10;

nsMediaDecoder::nsMediaDecoder() :
  mElement(nullptr),
  mFrameBufferLength(0),
  mPinnedForSeek(false),
  mShuttingDown(false)
{
  MOZ_COUNT_CTOR(nsMediaDecoder);
  MediaMemoryReporter::AddMediaDecoder(this);
}

nsMediaDecoder::~nsMediaDecoder()
{
  MOZ_COUNT_DTOR(nsMediaDecoder);
  MediaMemoryReporter::RemoveMediaDecoder(this);
}

bool nsMediaDecoder::Init(nsHTMLMediaElement* aElement)
{
  mElement = aElement;
  mVideoFrameContainer = aElement->GetVideoFrameContainer();
  return true;
}

void nsMediaDecoder::Shutdown()
{
  StopProgress();
  mElement = nullptr;
}

nsHTMLMediaElement* nsMediaDecoder::GetMediaElement()
{
  return mElement;
}

nsresult nsMediaDecoder::RequestFrameBufferLength(PRUint32 aLength)
{
  if (aLength < FRAMEBUFFER_LENGTH_MIN || aLength > FRAMEBUFFER_LENGTH_MAX) {
    return NS_ERROR_DOM_INDEX_SIZE_ERR;
  }

  mFrameBufferLength = aLength;
  return NS_OK;
}

static void ProgressCallback(nsITimer* aTimer, void* aClosure)
{
  nsMediaDecoder* decoder = static_cast<nsMediaDecoder*>(aClosure);
  decoder->Progress(true);
}

void nsMediaDecoder::Progress(bool aTimer)
{
  if (!mElement)
    return;

  TimeStamp now = TimeStamp::Now();

  if (!aTimer) {
    mDataTime = now;
  }

  // If PROGRESS_MS has passed since the last progress event fired and more
  // data has arrived since then, fire another progress event.
  if ((mProgressTime.IsNull() ||
       now - mProgressTime >= TimeDuration::FromMilliseconds(PROGRESS_MS)) &&
      !mDataTime.IsNull() &&
      now - mDataTime <= TimeDuration::FromMilliseconds(PROGRESS_MS)) {
    mElement->DispatchAsyncEvent(NS_LITERAL_STRING("progress"));
    mProgressTime = now;
  }

  if (!mDataTime.IsNull() &&
      now - mDataTime >= TimeDuration::FromMilliseconds(STALL_MS)) {
    mElement->DownloadStalled();
    // Null it out
    mDataTime = TimeStamp();
  }
}

nsresult nsMediaDecoder::StartProgress()
{
  if (mProgressTimer)
    return NS_OK;

  mProgressTimer = do_CreateInstance("@mozilla.org/timer;1");
  return mProgressTimer->InitWithFuncCallback(ProgressCallback,
                                              this,
                                              PROGRESS_MS,
                                              nsITimer::TYPE_REPEATING_SLACK);
}

nsresult nsMediaDecoder::StopProgress()
{
  if (!mProgressTimer)
    return NS_OK;

  nsresult rv = mProgressTimer->Cancel();
  mProgressTimer = nullptr;

  return rv;
}

void nsMediaDecoder::FireTimeUpdate()
{
  if (!mElement)
    return;
  mElement->FireTimeUpdate(true);
}

void nsMediaDecoder::PinForSeek()
{
  MediaResource* resource = GetResource();
  if (!resource || mPinnedForSeek) {
    return;
  }
  mPinnedForSeek = true;
  resource->Pin();
}

void nsMediaDecoder::UnpinForSeek()
{
  MediaResource* resource = GetResource();
  if (!resource || !mPinnedForSeek) {
    return;
  }
  mPinnedForSeek = false;
  resource->Unpin();
}

bool nsMediaDecoder::CanPlayThrough()
{
  Statistics stats = GetStatistics();
  if (!stats.mDownloadRateReliable || !stats.mPlaybackRateReliable) {
    return false;
  }
  PRInt64 bytesToDownload = stats.mTotalBytes - stats.mDownloadPosition;
  PRInt64 bytesToPlayback = stats.mTotalBytes - stats.mPlaybackPosition;
  double timeToDownload = bytesToDownload / stats.mDownloadRate;
  double timeToPlay = bytesToPlayback / stats.mPlaybackRate;

  if (timeToDownload > timeToPlay) {
    // Estimated time to download is greater than the estimated time to play.
    // We probably can't play through without having to stop to buffer.
    return false;
  }

  // Estimated time to download is less than the estimated time to play.
  // We can probably play through without having to buffer, but ensure that
  // we've got a reasonable amount of data buffered after the current
  // playback position, so that if the bitrate of the media fluctuates, or if
  // our download rate or decode rate estimation is otherwise inaccurate,
  // we don't suddenly discover that we need to buffer. This is particularly
  // required near the start of the media, when not much data is downloaded.
  PRInt64 readAheadMargin =
    static_cast<PRInt64>(stats.mPlaybackRate * CAN_PLAY_THROUGH_MARGIN);
  return stats.mTotalBytes == stats.mDownloadPosition ||
         stats.mDownloadPosition > stats.mPlaybackPosition + readAheadMargin;
}

namespace mozilla {

MediaMemoryReporter* MediaMemoryReporter::sUniqueInstance;

NS_MEMORY_REPORTER_IMPLEMENT(MediaDecodedVideoMemory,
  "explicit/media/decoded-video",
  KIND_HEAP,
  UNITS_BYTES,
  MediaMemoryReporter::GetDecodedVideoMemory,
  "Memory used by decoded video frames.")

NS_MEMORY_REPORTER_IMPLEMENT(MediaDecodedAudioMemory,
  "explicit/media/decoded-audio",
  KIND_HEAP,
  UNITS_BYTES,
  MediaMemoryReporter::GetDecodedAudioMemory,
  "Memory used by decoded audio chunks.")

MediaMemoryReporter::MediaMemoryReporter()
  : mMediaDecodedVideoMemory(new NS_MEMORY_REPORTER_NAME(MediaDecodedVideoMemory))
  , mMediaDecodedAudioMemory(new NS_MEMORY_REPORTER_NAME(MediaDecodedAudioMemory))
{
  NS_RegisterMemoryReporter(mMediaDecodedVideoMemory);
  NS_RegisterMemoryReporter(mMediaDecodedAudioMemory);
}

MediaMemoryReporter::~MediaMemoryReporter()
{
  NS_UnregisterMemoryReporter(mMediaDecodedVideoMemory);
  NS_UnregisterMemoryReporter(mMediaDecodedAudioMemory);
}

} // namespace mozilla