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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-*/
/* 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 */
#include "AudioSampleFormat.h"
#include "CubebUtils.h"
#include "MainThreadUtils.h"
#include "MediaSegment.h"
#include "mozilla/LinkedList.h"
#include "mozilla/Maybe.h"
#include "mozilla/Mutex.h"
#include "mozilla/StateWatching.h"
#include "mozilla/TaskQueue.h"
#include "nsAutoRef.h"
#include "nsIRunnable.h"
#include "nsTArray.h"
#include <speex/speex_resampler.h>
class nsIRunnable;
class nsIGlobalObject;
class nsPIDOMWindowInner;
namespace mozilla {
class AsyncLogger;
class AudioCaptureTrack;
class CrossGraphTransmitter;
class CrossGraphReceiver;
class NativeInputTrack;
}; // namespace mozilla
extern mozilla::AsyncLogger gMTGTraceLogger;
template <>
class nsAutoRefTraits<SpeexResamplerState>
: public nsPointerRefTraits<SpeexResamplerState> {
static void Release(SpeexResamplerState* aState) {
namespace mozilla {
extern LazyLogModule gMediaTrackGraphLog;
namespace dom {
enum class AudioContextOperation : uint8_t;
enum class AudioContextOperationFlags;
enum class AudioContextState : uint8_t;
} // namespace dom
* MediaTrackGraph is a framework for synchronized audio/video processing
* and playback. It is designed to be used by other browser components such as
* HTML media elements, media capture APIs, real-time media streaming APIs,
* multitrack media APIs, and advanced audio APIs.
* The MediaTrackGraph uses a dedicated thread to process media --- the media
* graph thread. This ensures that we can process media through the graph
* without blocking on main-thread activity. The media graph is only modified
* on the media graph thread, to ensure graph changes can be processed without
* interfering with media processing. All interaction with the media graph
* thread is done with message passing.
* APIs that modify the graph or its properties are described as "control APIs".
* These APIs are asynchronous; they queue graph changes internally and
* those changes are processed all-at-once by the MediaTrackGraph. The
* MediaTrackGraph monitors the main thread event loop via
* nsIAppShell::RunInStableState to ensure that graph changes from a single
* event loop task are always processed all together. Control APIs should only
* be used on the main thread, currently; we may be able to relax that later.
* To allow precise synchronization of times in the control API, the
* MediaTrackGraph maintains a "media timeline". Control APIs that take or
* return times use that timeline. Those times never advance during
* an event loop task. This time is returned by
* MediaTrackGraph::GetCurrentTime().
* Media decoding, audio processing and media playback use thread-safe APIs to
* the media graph to ensure they can continue while the main thread is blocked.
* When the graph is changed, we may need to throw out buffered data and
* reprocess it. This is triggered automatically by the MediaTrackGraph.
class AudioProcessingTrack;
class AudioNodeEngine;
class AudioNodeExternalInputTrack;
class AudioNodeTrack;
class DirectMediaTrackListener;
class ForwardedInputTrack;
class MediaInputPort;
class MediaTrack;
class MediaTrackGraph;
class MediaTrackGraphImpl;
class MediaTrackListener;
class DeviceInputConsumerTrack;
class DeviceInputTrack;
class ProcessedMediaTrack;
class SourceMediaTrack;
class AudioDataListenerInterface {
// Protected destructor, to discourage deletion outside of Release():
virtual ~AudioDataListenerInterface() = default;
* Number of audio input channels.
virtual uint32_t RequestedInputChannelCount(
MediaTrackGraph* aGraph) const = 0;
* The input processing params this listener wants the platform to apply.
virtual cubeb_input_processing_params RequestedInputProcessingParams(
MediaTrackGraph* aGraph) const = 0;
* Whether the underlying audio device is used for voice input.
virtual bool IsVoiceInput(MediaTrackGraph* aGraph) const = 0;
* Called when the underlying audio device has changed.
virtual void DeviceChanged(MediaTrackGraph* aGraph) = 0;
* Called when the underlying audio device is being closed.
virtual void Disconnect(MediaTrackGraph* aGraph) = 0;
* Called after an attempt to set the input processing params on the
* underlying input track.
virtual void NotifySetRequestedInputProcessingParamsResult(
MediaTrackGraph* aGraph, cubeb_input_processing_params aRequestedParams,
const Result<cubeb_input_processing_params, int>& aResult) = 0;
class AudioDataListener : public AudioDataListenerInterface {
// Protected destructor, to discourage deletion outside of Release():
virtual ~AudioDataListener() = default;
* This is a base class for main-thread listener callbacks.
* This callback is invoked on the main thread when the main-thread-visible
* state of a track has changed.
* These methods are called with the media graph monitor held, so
* reentry into general media graph methods is not possible.
* You should do something non-blocking and non-reentrant (e.g. dispatch an
* event) and return. NS_DispatchToCurrentThread would be a good choice.
* The listener is allowed to synchronously remove itself from the track, but
* not add or remove any other listeners.
class MainThreadMediaTrackListener {
virtual void NotifyMainThreadTrackEnded() = 0;
* Helper struct used to keep track of memory usage by AudioNodes.
struct AudioNodeSizes {
AudioNodeSizes() : mTrack(0), mEngine(0), mNodeType() {}
size_t mTrack;
size_t mEngine;
const char* mNodeType;
* Describes how a track should be disabled.
* ENABLED Not disabled.
* SILENCE_BLACK Audio data is turned into silence, video frames are made
* black.
* SILENCE_FREEZE Audio data is turned into silence, video freezes at
* last frame.
enum class DisabledTrackMode { ENABLED, SILENCE_BLACK, SILENCE_FREEZE };
* A track of audio or video data. The media type must be known at construction
* and cannot change. All tracks progress at the same rate --- "real time".
* Tracks cannot seek. The only operation readers can perform on a track is to
* read the next data.
* Consumers of a track can be reading from it at different offsets, but that
* should only happen due to the order in which consumers are being run.
* Those offsets must not diverge in the long term, otherwise we would require
* unbounded buffering.
* (DEPRECATED to be removed in bug 1581074)
* Tracks can be in a "blocked" state. While blocked, a track does not
* produce data. A track can be explicitly blocked via the control API,
* or implicitly blocked by whatever's generating it (e.g. an underrun in the
* source resource), or implicitly blocked because something consuming it
* blocks, or implicitly because it has ended.
* A track can be in an "ended" state. "Ended" tracks are permanently blocked.
* The "ended" state is terminal.
* Transitions into and out of the "blocked" and "ended" states are managed
* by the MediaTrackGraph on the media graph thread.
* We buffer media data ahead of the consumers' reading offsets. It is possible
* to have buffered data but still be blocked.
* Any track can have its audio or video playing when requested. The media
* track graph plays audio by constructing audio output tracks as necessary.
* Video is played through a DirectMediaTrackListener managed by
* VideoStreamTrack.
* The data in a track is managed by mSegment. The segment starts at GraphTime
* mStartTime and encodes its own TrackTime duration.
* Tracks are explicitly managed. The client creates them via
* MediaTrackGraph::Create{Source|ForwardedInput}Track, and releases them by
* calling Destroy() when no longer needed (actual destruction will be
* deferred). The actual object is owned by the MediaTrackGraph. The basic idea
* is that main thread objects will keep Tracks alive as long as necessary
* (using the cycle collector to clean up whenever needed).
* We make them refcounted only so that track-related messages with
* MediaTrack* pointers can be sent to the main thread safely.
* The lifetimes of MediaTracks are controlled from the main thread.
* For MediaTracks exposed to the DOM, the lifetime is controlled by the DOM
* wrapper; the DOM wrappers own their associated MediaTracks. When a DOM
* wrapper is destroyed, it sends a Destroy message for the associated
* MediaTrack and clears its reference (the last main-thread reference to
* the object). When the Destroy message is processed on the graph thread we
* immediately release the affected objects (disentangling them from other
* objects as necessary).
* This could cause problems for media processing if a MediaTrack is destroyed
* while a downstream MediaTrack is still using it. Therefore the DOM wrappers
* must keep upstream MediaTracks alive as long as they could be used in the
* media graph.
* At any time, however, a set of MediaTrack wrappers could be collected via
* cycle collection. Destroy messages will be sent for those objects in
* arbitrary order and the MediaTrackGraph has to be able to handle this.
class MediaTrack : public mozilla::LinkedListElement<MediaTrack> {
MediaTrack(TrackRate aSampleRate, MediaSegment::Type aType,
MediaSegment* aSegment);
// The sample rate of the graph.
const TrackRate mSampleRate;
const MediaSegment::Type mType;
// Protected destructor, to discourage deletion outside of Release():
virtual ~MediaTrack();
* Returns the graph that owns this track.
MediaTrackGraphImpl* GraphImpl();
const MediaTrackGraphImpl* GraphImpl() const;
MediaTrackGraph* Graph() { return mGraph; }
const MediaTrackGraph* Graph() const { return mGraph; }
* Sets the graph that owns this track. Should only be called once.
void SetGraphImpl(MediaTrackGraphImpl* aGraph);
void SetGraphImpl(MediaTrackGraph* aGraph);
// Control API.
void AddAudioOutput(void* aKey, const AudioDeviceInfo* aSink);
void AddAudioOutput(void* aKey, CubebUtils::AudioDeviceID aDeviceID,
TrackRate aPreferredSampleRate);
void SetAudioOutputVolume(void* aKey, float aVolume);
void RemoveAudioOutput(void* aKey);
// Explicitly suspend. Useful for example if a media element is pausing
// and we need to stop its track emitting its buffered data. As soon as the
// Suspend message reaches the graph, the track stops processing. It
// ignores its inputs and produces silence/no video until Resumed. Its
// current time does not advance.
void Suspend();
void Resume();
// Events will be dispatched by calling methods of aListener.
virtual void AddListener(MediaTrackListener* aListener);
virtual RefPtr<GenericPromise> RemoveListener(MediaTrackListener* aListener);
* Adds aListener to the source track of this track.
* When the MediaTrackGraph processes the added listener, it will traverse
* the graph and add it to the track's source track.
* Note that the listener will be notified on the MediaTrackGraph thread
* with whether the installation of it at the source was successful or not.
void AddDirectListener(DirectMediaTrackListener* aListener);
* Removes aListener from the source track of this track.
* Note that the listener has already been removed if the link between the
* source and this track has been broken. The caller doesn't have to care
* about this, removing when the source cannot be found, or when the listener
* had already been removed does nothing.
void RemoveDirectListener(DirectMediaTrackListener* aListener);
// A disabled track has video replaced by black, and audio replaced by
// silence.
void SetDisabledTrackMode(DisabledTrackMode aMode);
// End event will be notified by calling methods of aListener. It is the
// responsibility of the caller to remove aListener before it is destroyed.
void AddMainThreadListener(MainThreadMediaTrackListener* aListener);
// It's safe to call this even if aListener is not currently a listener;
// the call will be ignored.
void RemoveMainThreadListener(MainThreadMediaTrackListener* aListener) {
* Append to the message queue a control message to execute a given lambda
* function with no parameters. The queue is drained during
* RunInStableState(). The lambda will be executed on the graph thread.
* The lambda will not be executed if the graph has been forced to shut
* down.
template <typename Function>
void QueueControlMessageWithNoShutdown(Function&& aFunction) {
new ControlMessageWithNoShutdown(std::forward<Function>(aFunction))));
enum class IsInShutdown { No, Yes };
* Append to the message queue a control message to execute a given lambda
* function with a single IsInShutdown parameter. A No argument indicates
* execution on the thread of a graph that is still running. A Yes argument
* indicates execution on the main thread when the graph has been forced to
* shut down.
template <typename Function>
void QueueControlOrShutdownMessage(Function&& aFunction) {
new ControlOrShutdownMessage(std::forward<Function>(aFunction))));
* Ensure a runnable will run on the main thread after running all pending
* updates that were sent from the graph thread or will be sent before the
* graph thread receives the next graph update.
* If the graph has been shut down or destroyed, then the runnable will be
* dispatched to the event queue immediately. (There are no pending updates
* in this situation.)
* Main thread only.
void RunAfterPendingUpdates(already_AddRefed<nsIRunnable> aRunnable);
// Signal that the client is done with this MediaTrack. It will be deleted
// later.
virtual void Destroy();
// Returns the main-thread's view of how much data has been processed by
// this track.
TrackTime GetCurrentTime() const {
NS_ASSERTION(NS_IsMainThread(), "Call only on main thread");
return mMainThreadCurrentTime;
// Return the main thread's view of whether this track has ended.
bool IsEnded() const {
NS_ASSERTION(NS_IsMainThread(), "Call only on main thread");
return mMainThreadEnded;
bool IsDestroyed() const {
NS_ASSERTION(NS_IsMainThread(), "Call only on main thread");
return mMainThreadDestroyed;
friend class MediaTrackGraphImpl;
friend class MediaInputPort;
friend class AudioNodeExternalInputTrack;
virtual AudioProcessingTrack* AsAudioProcessingTrack() { return nullptr; }
virtual SourceMediaTrack* AsSourceTrack() { return nullptr; }
virtual ProcessedMediaTrack* AsProcessedTrack() { return nullptr; }
virtual AudioNodeTrack* AsAudioNodeTrack() { return nullptr; }
virtual ForwardedInputTrack* AsForwardedInputTrack() { return nullptr; }
virtual CrossGraphTransmitter* AsCrossGraphTransmitter() { return nullptr; }
virtual CrossGraphReceiver* AsCrossGraphReceiver() { return nullptr; }
virtual DeviceInputTrack* AsDeviceInputTrack() { return nullptr; }
virtual DeviceInputConsumerTrack* AsDeviceInputConsumerTrack() {
return nullptr;
// These Impl methods perform the core functionality of the control methods
// above, on the media graph thread.
* Stop all track activity and disconnect it from all inputs and outputs.
* This must be idempotent.
virtual void DestroyImpl();
TrackTime GetEnd() const;
* Removes all direct listeners and signals to them that they have been
* uninstalled.
virtual void RemoveAllDirectListenersImpl() {}
void RemoveAllResourcesAndListenersImpl();
virtual void AddListenerImpl(already_AddRefed<MediaTrackListener> aListener);
virtual void RemoveListenerImpl(MediaTrackListener* aListener);
virtual void AddDirectListenerImpl(
already_AddRefed<DirectMediaTrackListener> aListener);
virtual void RemoveDirectListenerImpl(DirectMediaTrackListener* aListener);
virtual void SetDisabledTrackModeImpl(DisabledTrackMode aMode);
void AddConsumer(MediaInputPort* aPort) { mConsumers.AppendElement(aPort); }
void RemoveConsumer(MediaInputPort* aPort) {
GraphTime StartTime() const { return mStartTime; }
bool Ended() const { return mEnded; }
// Returns the current number of channels this track contains if it's an audio
// track. Calling this on a video track will trip assertions. Graph thread
// only.
virtual uint32_t NumberOfChannels() const = 0;
// The DisabledTrackMode after combining the explicit mode and that of the
// input, if any.
virtual DisabledTrackMode CombinedDisabledMode() const {
return mDisabledMode;
template <class SegmentType>
SegmentType* GetData() const {
if (!mSegment) {
return nullptr;
if (mSegment->GetType() != SegmentType::StaticType()) {
return nullptr;
return static_cast<SegmentType*>(mSegment.get());
MediaSegment* GetData() const { return mSegment.get(); }
double TrackTimeToSeconds(TrackTime aTime) const {
NS_ASSERTION(0 <= aTime && aTime <= TRACK_TIME_MAX, "Bad time");
return static_cast<double>(aTime) / mSampleRate;
int64_t TrackTimeToMicroseconds(TrackTime aTime) const {
NS_ASSERTION(0 <= aTime && aTime <= TRACK_TIME_MAX, "Bad time");
return (aTime * 1000000) / mSampleRate;
TrackTime SecondsToNearestTrackTime(double aSeconds) const {
"Bad seconds");
return mSampleRate * aSeconds + 0.5;
TrackTime MicrosecondsToTrackTimeRoundDown(int64_t aMicroseconds) const {
return (aMicroseconds * mSampleRate) / 1000000;
TrackTicks TimeToTicksRoundUp(TrackRate aRate, TrackTime aTime) const {
return RateConvertTicksRoundUp(aRate, mSampleRate, aTime);
TrackTime TicksToTimeRoundDown(TrackRate aRate, TrackTicks aTicks) const {
return RateConvertTicksRoundDown(mSampleRate, aRate, aTicks);
* Convert graph time to track time. aTime must be <= mStateComputedTime
* to ensure we know exactly how much time this track will be blocked during
* the interval.
TrackTime GraphTimeToTrackTimeWithBlocking(GraphTime aTime) const;
* Convert graph time to track time. This assumes there is no blocking time
* to take account of, which is always true except between a track
* having its blocking time calculated in UpdateGraph and its blocking time
* taken account of in UpdateCurrentTimeForTracks.
TrackTime GraphTimeToTrackTime(GraphTime aTime) const;
* Convert track time to graph time. This assumes there is no blocking time
* to take account of, which is always true except between a track
* having its blocking time calculated in UpdateGraph and its blocking time
* taken account of in UpdateCurrentTimeForTracks.
GraphTime TrackTimeToGraphTime(TrackTime aTime) const;
virtual void ApplyTrackDisabling(MediaSegment* aSegment,
MediaSegment* aRawSegment = nullptr);
// Return true if the main thread needs to observe updates from this track.
virtual bool MainThreadNeedsUpdates() const { return true; }
virtual size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const;
virtual size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const;
bool IsSuspended() const { return mSuspendedCount > 0; }
* Increment suspend count and move it to GraphImpl()->mSuspendedTracks if
* necessary. Graph thread.
void IncrementSuspendCount();
* Increment suspend count on aTrack and move it to GraphImpl()->mTracks if
* necessary. GraphThread.
virtual void DecrementSuspendCount();
void AssertOnGraphThread() const;
void AssertOnGraphThreadOrNotRunning() const;
* For use during ProcessedMediaTrack::ProcessInput() or
* MediaTrackListener callbacks, when graph state cannot be changed.
* Queues a control message to execute a given lambda function with no
* parameters after processing, at a time when graph state can be changed.
* The lambda will always be executed before handing control of the graph
* to the main thread for shutdown.
* Graph thread.
template <typename Function>
void RunAfterProcessing(Function&& aFunction) {
new ControlMessageWithNoShutdown(std::forward<Function>(aFunction))));
class ControlMessageInterface;
// Called on graph thread either during destroy handling or before handing
// graph control to the main thread to release tracks.
virtual void OnGraphThreadDone() {}
// |AdvanceTimeVaryingValuesToCurrentTime| will be override in
// SourceMediaTrack.
virtual void AdvanceTimeVaryingValuesToCurrentTime(GraphTime aCurrentTime,
GraphTime aBlockedTime);
template <typename Function>
class ControlMessageWithNoShutdown;
template <typename Function>
class ControlOrShutdownMessage;
void QueueMessage(UniquePtr<ControlMessageInterface> aMessage);
void RunMessageAfterProcessing(UniquePtr<ControlMessageInterface> aMessage);
void NotifyMainThreadListeners() {
NS_ASSERTION(NS_IsMainThread(), "Call only on main thread");
for (int32_t i = mMainThreadListeners.Length() - 1; i >= 0; --i) {
bool ShouldNotifyTrackEnded() {
NS_ASSERTION(NS_IsMainThread(), "Call only on main thread");
if (!mMainThreadEnded || mEndedNotificationSent) {
return false;
mEndedNotificationSent = true;
return true;
// Notifies listeners and consumers of the change in disabled mode when the
// current combined mode is different from aMode.
void NotifyIfDisabledModeChangedFrom(DisabledTrackMode aOldMode);
// This state is all initialized on the main thread but
// otherwise modified only on the media graph thread.
// Buffered data. The start of the buffer corresponds to mStartTime.
// Conceptually the buffer contains everything this track has ever played,
// but we forget some prefix of the buffered data to bound the space usage.
// Note that this may be null for tracks that never contain data, like
// non-external AudioNodeTracks.
const UniquePtr<MediaSegment> mSegment;
// The time when the buffered data could be considered to have started
// playing. This increases over time to account for time the track was
// blocked before mCurrentTime.
GraphTime mStartTime;
// The time until which we last called mSegment->ForgetUpTo().
TrackTime mForgottenTime;
// True once we've processed mSegment until the end and no more data will be
// added. Note that mSegment might still contain data for the current
// iteration.
bool mEnded;
// True after track listeners have been notified that this track has ended.
bool mNotifiedEnded;
// Client-set volume of this track
nsTArray<RefPtr<MediaTrackListener>> mTrackListeners;
nsTArray<MainThreadMediaTrackListener*> mMainThreadListeners;
// This track's associated disabled mode. It can either by disabled by frames
// being replaced by black, or by retaining the previous frame.
DisabledTrackMode mDisabledMode;
// GraphTime at which this track starts blocking.
// This is only valid up to mStateComputedTime. The track is considered to
// have not been blocked before mCurrentTime (its mStartTime is
// increased as necessary to account for that time instead).
GraphTime mStartBlocking;
// MediaInputPorts to which this is connected
nsTArray<MediaInputPort*> mConsumers;
* Number of outstanding suspend operations on this track. Track is
* suspended when this is > 0.
int32_t mSuspendedCount;
// Main-thread views of state
TrackTime mMainThreadCurrentTime;
bool mMainThreadEnded;
bool mEndedNotificationSent;
bool mMainThreadDestroyed;
// Our media track graph. null if destroyed on the graph thread.
MediaTrackGraph* mGraph;
* This is a track into which a decoder can write audio or video.
* Audio or video can be written on any thread, but you probably want to
* always write from the same thread to avoid unexpected interleavings.
* For audio the sample rate of the written data can differ from the sample rate
* of the graph itself. Use SetAppendDataSourceRate to inform the track what
* rate written audio data will be sampled in.
class SourceMediaTrack : public MediaTrack {
SourceMediaTrack(MediaSegment::Type aType, TrackRate aSampleRate);
SourceMediaTrack* AsSourceTrack() override { return this; }
// Main thread only
* Enable or disable pulling.
* When pulling is enabled, NotifyPull gets called on the
* MediaTrackListeners for this track during the MediaTrackGraph
* control loop. Pulling is initially disabled. Due to unavoidable race
* conditions, after a call to SetPullingEnabled(false) it is still possible
* for a NotifyPull to occur.
void SetPullingEnabled(bool aEnabled);
// MediaTrackGraph thread only
void DestroyImpl() override;
// Call these on any thread.
* Call all MediaTrackListeners to request new data via the NotifyPull
* API (if enabled).
* aDesiredUpToTime (in): end time of new data requested.
* Returns true if new data is about to be added.
bool PullNewData(GraphTime aDesiredUpToTime);
* Extract any state updates pending in the track, and apply them.
void ExtractPendingInput(GraphTime aCurrentTime, GraphTime aDesiredUpToTime);
* All data appended with AppendData() from this point on will be resampled
* from aRate to the graph rate.
* Resampling for video does not make sense and is forbidden.
void SetAppendDataSourceRate(TrackRate aRate);
* Append media data to this track. Ownership of aSegment remains with the
* caller, but aSegment is emptied. Returns 0 if the data was not appended
* because the stream has ended. Returns the duration of the appended data in
* the graph's track rate otherwise.
TrackTime AppendData(MediaSegment* aSegment,
MediaSegment* aRawSegment = nullptr);
* Clear any data appended with AppendData() that hasn't entered the graph
* yet. Returns the duration of the cleared data in the graph's track rate.
TrackTime ClearFutureData();
* Indicate that this track has ended. Do not do any more API calls affecting
* this track.
void End();
void SetDisabledTrackModeImpl(DisabledTrackMode aMode) override;
uint32_t NumberOfChannels() const override;
void RemoveAllDirectListenersImpl() override;
// The value set here is applied in MoveToSegment so we can avoid the
// buffering delay in applying the change. See Bug 1443511.
void SetVolume(float aVolume);
float GetVolumeLocked() MOZ_REQUIRES(mMutex);
Mutex& GetMutex() MOZ_RETURN_CAPABILITY(mMutex) { return mMutex; }
friend class MediaTrackGraphImpl;
enum TrackCommands : uint32_t;
virtual ~SourceMediaTrack();
* Data to cater for appending media data to this track.
struct TrackData {
// Sample rate of the input data.
TrackRate mInputRate;
// Resampler if the rate of the input track does not match the
// MediaTrackGraph's.
nsAutoRef<SpeexResamplerState> mResampler;
uint32_t mResamplerChannelCount;
// Each time the track updates are flushed to the media graph thread,
// the segment buffer is emptied.
UniquePtr<MediaSegment> mData;
// True once the producer has signaled that no more data is coming.
bool mEnded;
// True if the producer of this track is having data pulled by the graph.
bool mPullingEnabled;
// True if the graph has notified this track that it will not be used
// again on the graph thread.
bool mGraphThreadDone;
bool NeedsMixing();
void ResampleAudioToGraphSampleRate(MediaSegment* aSegment)
void AddDirectListenerImpl(
already_AddRefed<DirectMediaTrackListener> aListener) override;
void RemoveDirectListenerImpl(DirectMediaTrackListener* aListener) override;
* Notify direct consumers of new data to this track.
* The data doesn't have to be resampled (though it may be). This is called
* from AppendData on the thread providing the data, and will call
* the Listeners on this thread.
void NotifyDirectConsumers(MediaSegment* aSegment) MOZ_REQUIRES(mMutex);
void OnGraphThreadDone() override {
MutexAutoLock lock(mMutex);
if (!mUpdateTrack) {
mUpdateTrack->mGraphThreadDone = true;
if (!mUpdateTrack->mData) {
virtual void AdvanceTimeVaryingValuesToCurrentTime(
GraphTime aCurrentTime, GraphTime aBlockedTime) override;
// This must be acquired *before* MediaTrackGraphImpl's lock, if they are
// held together.
Mutex mMutex;
// protected by mMutex
float mVolume MOZ_GUARDED_BY(mMutex) = 1.0;
UniquePtr<TrackData> mUpdateTrack MOZ_GUARDED_BY(mMutex);
// This track's associated disabled mode for uses on the producing thread.
// It can either by disabled by frames being replaced by black, or by
// retaining the previous frame.
DisabledTrackMode mDirectDisabledMode MOZ_GUARDED_BY(mMutex) =
nsTArray<RefPtr<DirectMediaTrackListener>> mDirectTrackListeners
* A ref-counted wrapper of a MediaTrack that allows multiple users to share a
* reference to the same MediaTrack with the purpose of being guaranteed that
* the graph it is in is kept alive.
* Automatically suspended on creation and destroyed on destruction. Main thread
* only.
struct SharedDummyTrack {
explicit SharedDummyTrack(MediaTrack* aTrack) : mTrack(aTrack) {
const RefPtr<MediaTrack> mTrack;
~SharedDummyTrack() { mTrack->Destroy(); }
* Represents a connection between a ProcessedMediaTrack and one of its
* input tracks.
* We make these refcounted so that track-related messages with MediaInputPort*
* pointers can be sent to the main thread safely.
* When a port's source or destination track dies, the track's DestroyImpl
* calls MediaInputPort::Disconnect to disconnect the port from
* the source and destination tracks.
* The lifetimes of MediaInputPort are controlled from the main thread.
* The media graph adds a reference to the port. When a MediaInputPort is no
* longer needed, main-thread code sends a Destroy message for the port and
* clears its reference (the last main-thread reference to the object). When
* the Destroy message is processed on the graph manager thread we disconnect
* the port and drop the graph's reference, destroying the object.
class MediaInputPort final {
// Do not call this constructor directly. Instead call
// aDest->AllocateInputPort.
MediaInputPort(MediaTrackGraphImpl* aGraph, MediaTrack* aSource,
ProcessedMediaTrack* aDest, uint16_t aInputNumber,
uint16_t aOutputNumber)
: mSource(aSource),
mGraph(aGraph) {
// Private destructor, to discourage deletion outside of Release():
* Disconnects and destroys the port. The caller must not reference this
* object again. Main thread.
void Destroy();
// The remaining methods and members must always be called on the graph thread
// from within MediaTrackGraph.cpp.
void Init();
// Called during message processing to trigger removal of this port's source
// and destination tracks.
void Disconnect();
MediaTrack* GetSource() const;
ProcessedMediaTrack* GetDestination() const;
uint16_t InputNumber() const { return mInputNumber; }
uint16_t OutputNumber() const { return mOutputNumber; }
struct InputInterval {
GraphTime mStart;
GraphTime mEnd;
bool mInputIsBlocked;
// Find the next time interval starting at or after aTime during which
// aPort->mDest is not blocked and aPort->mSource's blocking status does not
// change. A null aPort returns a blocked interval starting at aTime.
static InputInterval GetNextInputInterval(MediaInputPort const* aPort,
GraphTime aTime);
* Returns the graph that owns this port.
MediaTrackGraphImpl* GraphImpl() const;
MediaTrackGraph* Graph() const;
* Sets the graph that owns this track. Should only be called once.
void SetGraphImpl(MediaTrackGraphImpl* aGraph);
* Notify the port that the source MediaTrack has been suspended.
void Suspended();
* Notify the port that the source MediaTrack has been resumed.
void Resumed();
size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
size_t amount = 0;
// Not owned:
// - mSource
// - mDest
// - mGraph
return amount;
size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const {
return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
friend class ProcessedMediaTrack;
// Never modified after Init()
MediaTrack* mSource;
ProcessedMediaTrack* mDest;
// The input and output numbers are optional, and are currently only used by
// Web Audio.
const uint16_t mInputNumber;
const uint16_t mOutputNumber;
// Our media track graph
MediaTrackGraphImpl* mGraph;
* This track processes zero or more input tracks in parallel to produce
* its output. The details of how the output is produced are handled by
* subclasses overriding the ProcessInput method.
class ProcessedMediaTrack : public MediaTrack {
ProcessedMediaTrack(TrackRate aSampleRate, MediaSegment::Type aType,
MediaSegment* aSegment)
: MediaTrack(aSampleRate, aType, aSegment),
mCycleMarker(0) {}
// Control API.
* Allocates a new input port attached to source aTrack.
* This port can be removed by calling MediaInputPort::Destroy().
already_AddRefed<MediaInputPort> AllocateInputPort(
MediaTrack* aTrack, uint16_t aInputNumber = 0,
uint16_t aOutputNumber = 0);
* Queue a message to set the autoend flag on this track (defaults to
* true). When this flag is set, and the input track has ended playout
* (including if there is no input track), this track automatically
* enters the ended state.
virtual void QueueSetAutoend(bool aAutoend);
ProcessedMediaTrack* AsProcessedTrack() override { return this; }
friend class MediaTrackGraphImpl;
// Do not call these from outside MediaTrackGraph.cpp!
virtual void AddInput(MediaInputPort* aPort);
virtual void RemoveInput(MediaInputPort* aPort) {
mInputs.RemoveElement(aPort) || mSuspendedInputs.RemoveElement(aPort);
bool HasInputPort(MediaInputPort* aPort) const {
return mInputs.Contains(aPort) || mSuspendedInputs.Contains(aPort);
uint32_t InputPortCount() const {
return mInputs.Length() + mSuspendedInputs.Length();
void InputSuspended(MediaInputPort* aPort);
void InputResumed(MediaInputPort* aPort);
void DestroyImpl() override;
void DecrementSuspendCount() override;
* This gets called after we've computed the blocking states for all
* tracks (mBlocked is up to date up to mStateComputedTime).
* Also, we've produced output for all tracks up to this one. If this track
* is not in a cycle, then all its source tracks have produced data.
* Generate output from aFrom to aTo, where aFrom < aTo.
* This will be called on tracks that have ended. Most track types should
* just return immediately if they're ended, but some may wish to update
* internal state (see AudioNodeTrack).
* ProcessInput is allowed to set mEnded only if ALLOW_END is in aFlags. (This
* flag will be set when aTo >= mStateComputedTime, i.e. when we've produced
* the last block of data we need to produce.) Otherwise we can get into a
* situation where we've determined the track should not block before
* mStateComputedTime, but the track ends before mStateComputedTime, violating
* the invariant that ended tracks are blocked.
enum { ALLOW_END = 0x01 };
virtual void ProcessInput(GraphTime aFrom, GraphTime aTo,
uint32_t aFlags) = 0;
void SetAutoendImpl(bool aAutoend) { mAutoend = aAutoend; }
// Only valid after MediaTrackGraphImpl::UpdateTrackOrder() has run.
// A DelayNode is considered to break a cycle and so this will not return
// true for echo loops, only for muted cycles.
bool InMutedCycle() const { return mCycleMarker; }
// Used by ForwardedInputTrack to propagate the disabled mode along the graph.
virtual void OnInputDisabledModeChanged(DisabledTrackMode aMode) {}
size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const override {
size_t amount = MediaTrack::SizeOfExcludingThis(aMallocSizeOf);
// Not owned:
// - mInputs elements
// - mSuspendedInputs elements
amount += mInputs.ShallowSizeOfExcludingThis(aMallocSizeOf);
amount += mSuspendedInputs.ShallowSizeOfExcludingThis(aMallocSizeOf);
return amount;
size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const override {
return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
// This state is all accessed only on the media graph thread.
// The list of all inputs that are not currently suspended.
nsTArray<MediaInputPort*> mInputs;
// The list of all inputs that are currently suspended.
nsTArray<MediaInputPort*> mSuspendedInputs;
bool mAutoend;
// After UpdateTrackOrder(), mCycleMarker is either 0 or 1 to indicate
// whether this track is in a muted cycle. During ordering it can contain
// other marker values - see MediaTrackGraphImpl::UpdateTrackOrder().
uint32_t mCycleMarker;
* There is a single MediaTrackGraph per window.
* Additionaly, each OfflineAudioContext object creates its own MediaTrackGraph
* object too.
class MediaTrackGraph {
// We ensure that the graph current time advances in multiples of
// IdealAudioBlockSize()/AudioStream::PreferredSampleRate(). A track that
// never blocks and has the ideal audio rate will produce audio in multiples
// of the block size.
// Initializing a graph that outputs audio can take quite long on some
// platforms. Code that want to output audio at some point can express the
// fact that they will need an audio track at some point by passing
// AUDIO_THREAD_DRIVER when getting an instance of MediaTrackGraph, so that
// the graph starts with the right driver.
enum GraphDriverType {
// A MediaTrackGraph running an AudioWorklet must always be run from the
// same thread, in order to run js. To acheive this, create the graph with
// a SINGLE_THREAD RunType. DIRECT_DRIVER will run the graph directly off
// the GraphDriver's thread.
enum GraphRunType {
static const uint32_t AUDIO_CALLBACK_DRIVER_SHUTDOWN_TIMEOUT = 20 * 1000;
static const TrackRate REQUEST_DEFAULT_SAMPLE_RATE = 0;
constexpr static const CubebUtils::AudioDeviceID DEFAULT_OUTPUT_DEVICE =
// Main thread only
static MediaTrackGraph* GetInstanceIfExists(
nsPIDOMWindowInner* aWindow, TrackRate aSampleRate,
CubebUtils::AudioDeviceID aPrimaryOutputDeviceID);
static MediaTrackGraph* GetInstance(
GraphDriverType aGraphDriverRequested, nsPIDOMWindowInner* aWindow,
TrackRate aSampleRate, CubebUtils::AudioDeviceID aPrimaryOutputDeviceID);
static MediaTrackGraph* CreateNonRealtimeInstance(TrackRate aSampleRate);
// Idempotent
void ForceShutDown();
virtual void OpenAudioInput(DeviceInputTrack* aTrack) = 0;
virtual void CloseAudioInput(DeviceInputTrack* aTrack) = 0;
// Control API.
* Create a track that a media decoder (or some other source of
* media data, such as a camera) can write to.
SourceMediaTrack* CreateSourceTrack(MediaSegment::Type aType);
* Create a track that will forward data from its input track.
* A TrackUnionStream can have 0 or 1 input streams. Adding more than that is
* an error.
* A TrackUnionStream will end when autoending is enabled (default) and there
* is no input, or the input's source is ended. If there is no input and
* autoending is disabled, TrackUnionStream will continue to produce silence
* for audio or the last video frame for video.
ProcessedMediaTrack* CreateForwardedInputTrack(MediaSegment::Type aType);
* Create a track that will mix all its audio inputs.
AudioCaptureTrack* CreateAudioCaptureTrack();
CrossGraphTransmitter* CreateCrossGraphTransmitter(
CrossGraphReceiver* aReceiver);
CrossGraphReceiver* CreateCrossGraphReceiver(TrackRate aTransmitterRate);
* Add a new track to the graph. Main thread.
void AddTrack(MediaTrack* aTrack);
/* From the main thread, ask the MTG to resolve the returned promise when
* the device specified has started.
* A null aDeviceID indicates the default audio output device.
* The promise is rejected with NS_ERROR_INVALID_ARG if aSink does not
* correspond to any output devices used by the graph, or
* NS_ERROR_NOT_AVAILABLE if outputs to the device are removed or
* NS_ERROR_ILLEGAL_DURING_SHUTDOWN if the graph is force shut down
* before the promise could be resolved.
using GraphStartedPromise = GenericPromise;
virtual RefPtr<GraphStartedPromise> NotifyWhenDeviceStarted(
CubebUtils::AudioDeviceID aDeviceID) = 0;
/* From the main thread, suspend, resume or close an AudioContext. Calls
* are not counted. Even Resume calls can be more frequent than Suspend
* calls.
* aTracks are the tracks of all the AudioNodes of the AudioContext that
* need to be suspended or resumed. Suspend and Resume operations on these
* tracks are counted. Resume operations must not outnumber Suspends and a
* track will not resume until the number of Resume operations matches the
* number of Suspends. This array may be empty if, for example, this is a
* second consecutive suspend call and all the nodes are already suspended.
* This can possibly pause the graph thread, releasing system resources, if
* all tracks have been suspended/closed.
* When the operation is complete, the returned promise is resolved.
using AudioContextOperationPromise =
MozPromise<dom::AudioContextState, bool, true>;
RefPtr<AudioContextOperationPromise> ApplyAudioContextOperation(
MediaTrack* aDestinationTrack, nsTArray<RefPtr<MediaTrack>> aTracks,
dom::AudioContextOperation aOperation);
bool IsNonRealtime() const;
* Start processing non-realtime for a specific number of ticks.
void StartNonRealtimeProcessing(uint32_t aTicksToProcess);
* NotifyJSContext() is called on the graph thread before content script
* runs.
void NotifyJSContext(JSContext* aCx);
* Media graph thread only.
* Dispatches a runnable that will run on the main thread after all
* main-thread track state has been updated, i.e., during stable state.
* Should only be called during MediaTrackListener callbacks or during
* ProcessedMediaTrack::ProcessInput().
* Note that if called during shutdown the runnable will be ignored and
* released on main thread.
void DispatchToMainThreadStableState(already_AddRefed<nsIRunnable> aRunnable);
/* Called on the graph thread when the input device settings should be
* reevaluated, for example, if the channel count of the input track should
* be changed. */
void ReevaluateInputDevice(CubebUtils::AudioDeviceID aID);
* Returns graph sample rate in Hz.
TrackRate GraphRate() const { return mSampleRate; }
* Returns the ID of the device used for audio output through an
* AudioCallbackDriver. This is the device specified when creating the
* graph. Can be called on any thread.
CubebUtils::AudioDeviceID PrimaryOutputDeviceID() const {
return mPrimaryOutputDeviceID;
double AudioOutputLatency();
/* Return whether the clock for the audio output device used for the AEC
* reverse stream might drift from the clock for this MediaTrackGraph.
* Graph thread only. */
bool OutputForAECMightDrift();
void RegisterCaptureTrackForWindow(uint64_t aWindowId,
ProcessedMediaTrack* aCaptureTrack);
void UnregisterCaptureTrackForWindow(uint64_t aWindowId);
already_AddRefed<MediaInputPort> ConnectToCaptureTrack(
uint64_t aWindowId, MediaTrack* aMediaTrack);
void AssertOnGraphThread() const { MOZ_ASSERT(OnGraphThread()); }
void AssertOnGraphThreadOrNotRunning() const {
* Returns a watchable of the graph's main-thread observable graph time.
* Main thread only.
virtual Watchable<GraphTime>& CurrentTime() = 0;
* Graph thread function to return the time at which all processing has been
* completed. Some tracks may have performed processing beyond this time.
GraphTime ProcessedTime() const;
* For Graph thread logging.
void* CurrentDriver() const;
/* Do not call this directly. For users who need to get a DeviceInputTrack,
* use DeviceInputTrack::OpenAudio() instead. This should only be used in
* DeviceInputTrack to get the existing DeviceInputTrack paired with the given
* device in this graph. Main thread only.*/
DeviceInputTrack* GetDeviceInputTrackMainThread(
CubebUtils::AudioDeviceID aID);
/* Do not call this directly. This should only be used in DeviceInputTrack to
* get the existing NativeInputTrackMain thread only.*/
NativeInputTrack* GetNativeInputTrackMainThread();
explicit MediaTrackGraph(TrackRate aSampleRate,
CubebUtils::AudioDeviceID aPrimaryOutputDeviceID)
: mSampleRate(aSampleRate),
mPrimaryOutputDeviceID(aPrimaryOutputDeviceID) {
// Intended only for assertions, either on graph thread or not running (in
// which case we must be on the main thread).
virtual bool OnGraphThreadOrNotRunning() const = 0;
virtual bool OnGraphThread() const = 0;
// Intended only for internal assertions. Main thread only.
virtual bool Destroyed() const = 0;
* Sample rate at which this graph runs. For real time graphs, this is
* the rate of the audio mixer. For offline graphs, this is the rate specified
* at construction.
const TrackRate mSampleRate;
* Device to use for audio output through an AudioCallbackDriver.
* This is the device specified when creating the graph.
const CubebUtils::AudioDeviceID mPrimaryOutputDeviceID;
inline void MediaTrack::AssertOnGraphThread() const {
inline void MediaTrack::AssertOnGraphThreadOrNotRunning() const {
* This represents a message run on the graph thread to modify track or graph
* state. These are passed from main thread to graph thread by
* QueueControlMessageWithNoShutdown() or QueueControlOrShutdownMessage()
* through AppendMessage(), or scheduled on the graph thread with
* RunAfterProcessing().
class MediaTrack::ControlMessageInterface {
// All these run on the graph thread unless the graph has been forced to
// shut down.
// Do the action of this message on the MediaTrackGraph thread. Any actions
// affecting graph processing should take effect at mProcessedTime.
// All track data for times < mProcessedTime has already been
// computed.
virtual void Run() = 0;
// RunDuringShutdown() is only relevant to messages generated on the main
// thread by QueueControlOrShutdownMessage() or for AppendMessage().
// When we're shutting down the application, most messages are ignored but
// some cleanup messages should still be processed (on the main thread).
// This must not add new control messages to the graph.
virtual void RunDuringShutdown() {}
template <typename Function>
class MediaTrack::ControlMessageWithNoShutdown
: public ControlMessageInterface {
explicit ControlMessageWithNoShutdown(Function&& aFunction)
: mFunction(std::forward<Function>(aFunction)) {}
void Run() override {
"The lambda must return void!");
using StoredFunction = std::decay_t<Function>;
StoredFunction mFunction;
template <typename Function>
class MediaTrack::ControlOrShutdownMessage : public ControlMessageInterface {
explicit ControlOrShutdownMessage(Function&& aFunction)
: mFunction(std::forward<Function>(aFunction)) {}
void Run() override {
"The lambda must return void!");
void RunDuringShutdown() override { mFunction(IsInShutdown::Yes); }
// The same lambda is used whether or not in shutdown so that captured
// variables are available in both cases.
using StoredFunction = std::decay_t<Function>;
StoredFunction mFunction;
} // namespace mozilla