MediaStreamNote

MediaStream from getUserMedia

Call flow of getUserMedia:

Navigator::MozGetUserMedia(const MediaStreamConstraints& aConstraints,
                           NavigatorUserMediaSuccessCallback& aOnSuccess,
                           NavigatorUserMediaErrorCallback& aOnError,
                           ErrorResult& aRv)
{
  ...
  MediaManager* manager = MediaManager::Get();
  aRv = manager->GetUserMedia(privileged, mWindow, aConstraints,
                              onsuccess, onerror);
}

nsresult
MediaManager::GetUserMedia(bool aPrivileged,
  nsPIDOMWindow* aWindow, const MediaStreamConstraints& aConstraints,
  nsIDOMGetUserMediaSuccessCallback* aOnSuccess,
  nsIDOMGetUserMediaErrorCallback* aOnError)
{
  ...
  StreamListeners* listeners = GetActiveWindows()->Get(windowID);
  if (!listeners) {
    listeners = new StreamListeners;
    GetActiveWindows()->Put(windowID, listeners);
  }
  ...
    // Create a disabled listener to act as a placeholder
  GetUserMediaCallbackMediaStreamListener* listener =
    new GetUserMediaCallbackMediaStreamListener(mediaThread, windowID);

  // No need for locking because we always do this in the main thread.
  listeners->AppendElement(listener);
  ...
  // Pass callbacks and MediaStreamListener along to GetUserMediaRunnable.
  nsRefPtr<GetUserMediaRunnable> runnable;
  if (c.mFake) {
    // Fake stream from default backend.
    runnable = new GetUserMediaRunnable(c, onSuccess.forget(),
      onError.forget(), windowID, listener, mPrefs, new MediaEngineDefault());
  } else {
    // Stream from default device from WebRTC backend.
    runnable = new GetUserMediaRunnable(c, onSuccess.forget(),
      onError.forget(), windowID, listener, mPrefs);
  }
  ...
#ifdef MOZ_B2G_CAMERA
  if (mCameraManager == nullptr) {
    mCameraManager = nsDOMCameraManager::CreateInstance(aWindow);
  }
#endif
  ...
  if (aPrivileged ||
      (c.mFake && !Preferences::GetBool("media.navigator.permission.fake"))) {
    mMediaThread->Dispatch(runnable, NS_DISPATCH_NORMAL);
  } ...
}

NS_IMETHOD
GetUserMediaRunnable::Run()
{
  MediaEngine* backend = mBackend;
  // Was a backend provided?
  if (!backend) {
    // backend will become MediaEngineWebRTC.
    backend = mManager->GetBackend(mWindowID);
  }

  // Was a device provided?
  if (!mDeviceChosen) {
    // SelectDevice will call void MediaEngineWebRTC::EnumerateVideoDevices(MediaSourceType aMediaSource,
    //                                                                      nsTArray<nsRefPtr<MediaEngineVideoSource> >* aVSources).
    // It will new and append MediaEngineWebRTCVideoSource into aVSources.
    // Then pick the first devive.
    nsresult rv = SelectDevice(backend);
    if (rv != NS_OK) {
      return rv;
    }
  }
  ...
  ProcessGetUserMedia(((IsOn(mConstraints.mAudio) && mAudioDevice) ?
                       mAudioDevice->GetSource() : nullptr),
                      ((IsOn(mConstraints.mVideo) && mVideoDevice) ?
                       mVideoDevice->GetSource() : nullptr));
  return NS_OK;
}

void
ProcessGetUserMedia(MediaEngineAudioSource* aAudioSource,
                    MediaEngineVideoSource* aVideoSource)
{
  ...
  if (aVideoSource) {
    rv = aVideoSource->Allocate(GetInvariant(mConstraints.mVideo), mPrefs);
    ...
  }
  ...
  NS_DispatchToMainThread(new GetUserMediaStreamRunnable(
    mSuccess, mError, mWindowID, mListener, aAudioSource, aVideoSource,
    peerIdentity
  ));
  ...
}

NS_IMETHOD
GetUserMediaStreamRunnable::Run()
{
  ...
  // Create a media stream.
  nsRefPtr<nsDOMUserMediaStream> trackunion =
    nsDOMUserMediaStream::CreateTrackUnionStream(window, mAudioSource,
                                                 mVideoSource);
  ...
  MediaStreamGraph* gm = MediaStreamGraph::GetInstance();
  nsRefPtr<SourceMediaStream> stream = gm->CreateSourceStream(nullptr);
  ...
  trackunion->mSourceStream = stream;
  ...  
  // The listener was added at the beginning in an inactive state.
  // Activate our listener. We'll call Start() on the source when get a callback
  // that the MediaStream has started consuming. The listener is freed
  // when the page is invalidated (on navigation or close).
  mListener->Activate(stream.forget(), mAudioSource, mVideoSource);
  ...
  // This will call to nsresult MediaEngineWebRTCVideoSource::Start(SourceMediaStream* aStream, TrackID aID)
  nsRefPtr<MediaOperationRunnable> runnable(
    new MediaOperationRunnable(MEDIA_START, mListener, trackunion,
                               tracksAvailableCallback,
                               mAudioSource, mVideoSource, false, mWindowID,
                               mError.forget()));
  mediaThread->Dispatch(runnable, NS_DISPATCH_NORMAL);

  // We won't need mError now.
  mError = nullptr;
  return NS_OK;
}

SourceMediaStream*
MediaStreamGraph::CreateSourceStream(DOMMediaStream* aWrapper)
{
  SourceMediaStream* stream = new SourceMediaStream(aWrapper);
  NS_ADDREF(stream);
  MediaStreamGraphImpl* graph = static_cast<MediaStreamGraphImpl*>(this);
  stream->SetGraphImpl(graph);
  graph->AppendMessage(new CreateMessage(stream));
  return stream;
}

virtual void CreateMessage::Run() MOZ_OVERRIDE
{
  mStream->GraphImpl()->AddStream(mStream); // It will call mStreams.AppendElement(aStream);
  mStream->Init();
}