gecko-dev/content/media/fmp4/PlatformDecoderModule.h

/* -*- 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/. */

#if !defined(PlatformDecoderModule_h_)
#define PlatformDecoderModule_h_

#include "MediaDecoderReader.h"
#include "mozilla/layers/LayersTypes.h"
#include "nsTArray.h"
#include "mozilla/RefPtr.h"
#include <queue>

namespace mp4_demuxer {
class VideoDecoderConfig;
class AudioDecoderConfig;
struct MP4Sample;
}

class nsIThreadPool;

namespace mozilla {

namespace layers {
class ImageContainer;
}

class MediaDataDecoder;
class MediaDataDecoderCallback;
class MediaInputQueue;
class MediaTaskQueue;
typedef int64_t Microseconds;

// The PlatformDecoderModule interface is used by the MP4Reader to abstract
// access to the H264 and AAC decoders provided by various platforms. It
// may be extended to support other codecs in future. Each platform (Windows,
// MacOSX, Linux, B2G etc) must implement a PlatformDecoderModule to provide
// access to its decoders in order to get decompressed H.264/AAC from the
// MP4Reader.
//
// Video decoding is asynchronous, and should be performed on the task queue
// provided if the underlying platform isn't already exposing an async API.
//
// Platforms that don't have a corresponding PlatformDecoderModule won't be
// able to play the H.264/AAC data output by the MP4Reader. In practice this
// means that we won't have fragmented MP4 supported in Media Source
// Extensions.
//
// A cross-platform decoder module that discards input and produces "blank"
// output samples exists for testing, and is created when the pref
// "media.fragmented-mp4.use-blank-decoder" is true.
class PlatformDecoderModule {
public:
  // Call on the main thread to initialize the static state
  // needed by Create().
  static void Init();

  // Factory method that creates the appropriate PlatformDecoderModule for
  // the platform we're running on. Caller is responsible for deleting this
  // instance. It's expected that there will be multiple
  // PlatformDecoderModules alive at the same time. There is one
  // PlatformDecoderModule created per MP4Reader.
  // This is called on the decode thread.
  static PlatformDecoderModule* Create();

  // Called to shutdown the decoder module and cleanup state. This should
  // block until shutdown is complete. This is called after Shutdown() has
  // been called on all MediaDataDecoders created from this
  // PlatformDecoderModule.
  // Called on the main thread only.
  virtual nsresult Shutdown() = 0;

  // Creates an H.264 decoder. The layers backend is passed in so that
  // decoders can determine whether hardware accelerated decoding can be used.
  // Asynchronous decoding of video should be done in runnables dispatched
  // to aVideoTaskQueue. If the task queue isn't needed, the decoder should
  // not hold a reference to it.
  // Output and errors should be returned to the reader via aCallback.
  // On Windows the task queue's threads in have MSCOM initialized with
  // COINIT_MULTITHREADED.
  // Returns nullptr if the decoder can't be created.
  // It is safe to store a reference to aConfig.
  // Called on decode thread.
  virtual MediaDataDecoder* CreateH264Decoder(const mp4_demuxer::VideoDecoderConfig& aConfig,
                                              layers::LayersBackend aLayersBackend,
                                              layers::ImageContainer* aImageContainer,
                                              MediaTaskQueue* aVideoTaskQueue,
                                              MediaDataDecoderCallback* aCallback) = 0;

  // Creates an AAC decoder with the specified properties.
  // Asynchronous decoding of audio should be done in runnables dispatched to
  // aAudioTaskQueue. If the task queue isn't needed, the decoder should
  // not hold a reference to it.
  // Output and errors should be returned to the reader via aCallback.
  // Returns nullptr if the decoder can't be created.
  // On Windows the task queue's threads in have MSCOM initialized with
  // COINIT_MULTITHREADED.
  // It is safe to store a reference to aConfig.
  // Called on decode thread.
  virtual MediaDataDecoder* CreateAACDecoder(const mp4_demuxer::AudioDecoderConfig& aConfig,
                                             MediaTaskQueue* aAudioTaskQueue,
                                             MediaDataDecoderCallback* aCallback) = 0;

  virtual ~PlatformDecoderModule() {}

protected:
  PlatformDecoderModule() {}
  // Caches pref media.fragmented-mp4.use-blank-decoder
  static bool sUseBlankDecoder;
  static bool sFFmpegDecoderEnabled;
};

// A callback used by MediaDataDecoder to return output/errors to the
// MP4Reader. Implementation is threadsafe, and can be called on any thread.
class MediaDataDecoderCallback {
public:
  virtual ~MediaDataDecoderCallback() {}

  // Called by MediaDataDecoder when a sample has been decoded. Callee is
  // responsibile for deleting aData.
  virtual void Output(MediaData* aData) = 0;

  // Denotes an error in the decoding process. The reader will stop calling
  // the decoder.
  virtual void Error() = 0;

  // Denotes that the last input sample has been inserted into the decoder,
  // and no more output can be produced unless more input is sent.
  virtual void InputExhausted() = 0;
};

// MediaDataDecoder is the interface exposed by decoders created by the
// PlatformDecoderModule's Create*Decoder() functions. The type of
// media data that the decoder accepts as valid input and produces as
// output is determined when the MediaDataDecoder is created.
//
// All functions must be threadsafe, and be able to be called on an
// arbitrary thread.
//
// Decoding is done asynchronously. Any async work can be done on the
// MediaTaskQueue passed into the PlatformDecoderModules's Create*Decoder()
// function. This may not be necessary for platforms with async APIs
// for decoding.
class MediaDataDecoder {
protected:
  virtual ~MediaDataDecoder() {};

public:
  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(MediaDataDecoder)

  // Initialize the decoder. The decoder should be ready to decode after
  // this returns. The decoder should do any initialization here, rather
  // than in its constructor or PlatformDecoderModule::Create*Decoder(),
  // so that if the MP4Reader needs to shutdown during initialization,
  // it can call Shutdown() to cancel this operation. Any initialization
  // that requires blocking the calling thread in this function *must*
  // be done here so that it can be canceled by calling Shutdown()!
  virtual nsresult Init() = 0;

  // Inserts a sample into the decoder's decode pipeline. The decoder must
  // delete the sample once its been decoded. If Input() returns an error,
  // aSample will be deleted by the caller.
  virtual nsresult Input(mp4_demuxer::MP4Sample* aSample) = 0;

  // Causes all samples in the decoding pipeline to be discarded. When
  // this function returns, the decoder must be ready to accept new input
  // for decoding. This function is called when the demuxer seeks, before
  // decoding resumes after the seek.
  // While the reader calls Flush(), it ignores all output sent to it;
  // it is safe (but pointless) to send output while Flush is called.
  // The MP4Reader will not call Input() while it's calling Flush().
  virtual nsresult Flush() = 0;

  // Causes all complete samples in the pipeline that can be decoded to be
  // output. If the decoder can't produce samples from the current output,
  // it drops the input samples. The decoder may be holding onto samples
  // that are required to decode samples that it expects to get in future.
  // This is called when the demuxer reaches end of stream.
  // The MP4Reader will not call Input() while it's calling Drain().
  virtual nsresult Drain() = 0;

  // Cancels all init/input/drain operations, and shuts down the
  // decoder. The platform decoder should clean up any resources it's using
  // and release memory etc. Shutdown() must block until the decoder has
  // completed shutdown. The reader calls Flush() before calling Shutdown().
  // The reader will delete the decoder once Shutdown() returns.
  // The MediaDataDecoderCallback *must* not be called after Shutdown() has
  // returned.
  virtual nsresult Shutdown() = 0;

};

} // namespace mozilla

#endif