Bug 1324552 - Implement AudioContext baseLatency and outputLatency attributes. r=pehrsons,baku

Differential Revision: https://phabricator.services.mozilla.com/D37280

--HG--
extra : moz-landing-system : lando

dom/media/GraphDriver.cpp

@@ -1132,6 +1132,17 @@ void AudioCallbackDriver::CompleteAudioContextOperations(
   }
 }
 
+TimeDuration AudioCallbackDriver::AudioOutputLatency() {
+  uint32_t latency_frames;
+  int rv = cubeb_stream_get_latency(mAudioStream, &latency_frames);
+  if (rv || mSampleRate == 0) {
+    return TimeDuration::FromSeconds(0.0);
+  }
+
+  return TimeDuration::FromSeconds(static_cast<double>(latency_frames) /
+                                   mSampleRate);
+}
+
 void AudioCallbackDriver::FallbackToSystemClockDriver() {
   MOZ_ASSERT(!ThreadRunning());
   GraphImpl()->GetMonitor().AssertCurrentThreadOwns();

dom/media/GraphDriver.h

@@ -433,6 +433,9 @@ class AudioCallbackDriver : public GraphDriver,
 
   void CompleteAudioContextOperations(AsyncCubebOperation aOperation);
 
+  // Returns the output latency for the current audio output stream.
+  TimeDuration AudioOutputLatency();
+
  private:
   /* Remove Mixer callbacks when switching */
   void RemoveMixerCallback();

dom/media/MediaStreamGraph.cpp

@@ -957,6 +957,10 @@ void MediaStreamGraphImpl::DeviceChanged() {
     MediaStreamGraphImpl* mGraphImpl;
   };
 
+  // Reset the latency, it will get fetched again next time it's queried.
+  MOZ_ASSERT(NS_IsMainThread());
+  mAudioOutputLatency = 0.0;
+
   AppendMessage(MakeUnique<Message>(this));
 }
 
@@ -3192,7 +3196,8 @@ MediaStreamGraphImpl::MediaStreamGraphImpl(GraphDriverType aDriverRequested,
       mCanRunMessagesSynchronously(false)
 #endif
       ,
-      mMainThreadGraphTime(0, "MediaStreamGraphImpl::mMainThreadGraphTime") {
+      mMainThreadGraphTime(0, "MediaStreamGraphImpl::mMainThreadGraphTime"),
+      mAudioOutputLatency(0.0) {
   if (mRealtime) {
     if (aDriverRequested == AUDIO_THREAD_DRIVER) {
       // Always start with zero input channels, and no particular preferences
@@ -3796,6 +3801,29 @@ void MediaStreamGraph::ApplyAudioContextOperation(
       aDestinationStream, aStreams, aOperation, aPromise, aFlags));
 }
 
+double MediaStreamGraph::AudioOutputLatency() {
+  return static_cast<MediaStreamGraphImpl*>(this)->AudioOutputLatency();
+}
+
+double MediaStreamGraphImpl::AudioOutputLatency() {
+  MOZ_ASSERT(NS_IsMainThread());
+  if (mAudioOutputLatency != 0.0) {
+    return mAudioOutputLatency;
+  }
+  MonitorAutoLock lock(mMonitor);
+  if (CurrentDriver()->AsAudioCallbackDriver()) {
+    mAudioOutputLatency = CurrentDriver()
+                              ->AsAudioCallbackDriver()
+                              ->AudioOutputLatency()
+                              .ToSeconds();
+  } else {
+    // Failure mode: return 0.0 if running on a normal thread.
+    mAudioOutputLatency = 0.0;
+  }
+
+  return mAudioOutputLatency;
+}
+
 bool MediaStreamGraph::IsNonRealtime() const {
   return !static_cast<const MediaStreamGraphImpl*>(this)->mRealtime;
 }

dom/media/MediaStreamGraph.h

@@ -1272,6 +1272,8 @@ class MediaStreamGraph {
    */
   TrackRate GraphRate() const { return mSampleRate; }
 
+  double AudioOutputLatency();
+
   void RegisterCaptureStreamForWindow(uint64_t aWindowId,
                                       ProcessedMediaStream* aCaptureStream);
   void UnregisterCaptureStreamForWindow(uint64_t aWindowId);

dom/media/MediaStreamGraphImpl.h

@@ -453,6 +453,8 @@ class MediaStreamGraphImpl : public MediaStreamGraph,
 
   uint32_t AudioOutputChannelCount() const { return mOutputChannels; }
 
+  double AudioOutputLatency();
+
   /**
    * The audio input channel count for a MediaStreamGraph is the max of all the
    * channel counts requested by the listeners. The max channel count is
@@ -950,6 +952,12 @@ class MediaStreamGraphImpl : public MediaStreamGraph,
    * Read by stable state runnable on main thread. Protected by mMonitor.
    */
   GraphTime mNextMainThreadGraphTime = 0;
+
+  /**
+   * Cached audio output latency, in seconds. Main thread only. This is reset
+   * whenever the audio device running this MediaStreamGraph changes.
+   */
+  double mAudioOutputLatency;
 };
 
 }  // namespace mozilla

dom/media/webaudio/AudioContext.cpp

@@ -523,6 +523,8 @@ AudioListener* AudioContext::Listener() {
   return mListener;
 }
 
+double AudioContext::OutputLatency() { return Graph()->AudioOutputLatency(); }
+
 Worklet* AudioContext::GetAudioWorklet(ErrorResult& aRv) {
   if (!mWorklet) {
     mWorklet = AudioWorkletImpl::CreateWorklet(this, aRv);

dom/media/webaudio/AudioContext.h

@@ -192,6 +192,14 @@ class AudioContext final : public DOMEventTargetHelper,
 
   AudioContextState State() const { return mAudioContextState; }
 
+  double BaseLatency() const {
+    // Gecko does not do any buffering between rendering the audio and sending
+    // it to the audio subsystem.
+    return 0.0;
+  }
+
+  double OutputLatency();
+
   Worklet* GetAudioWorklet(ErrorResult& aRv);
 
   bool IsRunning() const;

dom/webidl/AudioContext.webidl

@@ -18,8 +18,9 @@ dictionary AudioContextOptions {
  Constructor(optional AudioContextOptions contextOptions = {})]
 interface AudioContext : BaseAudioContext {
 
-    // Bug 1324545: readonly        attribute double outputLatency;
     // Bug 1324545: AudioTimestamp                  getOutputTimestamp ();
+    readonly        attribute double               baseLatency;
+    readonly        attribute double               outputLatency;
 
     [Throws]
     Promise<void> suspend();

dom/webidl/BaseAudioContext.webidl

@@ -27,7 +27,6 @@ interface BaseAudioContext : EventTarget {
     readonly        attribute AudioContextState    state;
     [Throws, SameObject, SecureContext, Pref="dom.audioworklet.enabled"]
     readonly        attribute AudioWorklet         audioWorklet;
-    // Bug 1324552: readonly        attribute double               baseLatency;
 
     [Throws]
     Promise<void> resume();

testing/web-platform/meta/webaudio/idlharness.https.window.js.ini

@@ -74,9 +74,6 @@
   [AudioListener interface: context.listener must inherit property "forwardY" with the proper type]
     expected: FAIL
 
-  [AudioContext interface: context must inherit property "baseLatency" with the proper type]
-    expected: FAIL
-
   [MediaElementAudioSourceNode interface: attribute mediaElement]
     expected: FAIL
 
@@ -98,21 +95,12 @@
   [AudioParamMap must be primary interface of worklet_node.parameters]
     expected: FAIL
 
-  [AudioContext interface: context must inherit property "outputLatency" with the proper type]
-    expected: FAIL
-
   [OfflineAudioContext interface: operation suspend(double)]
     expected: FAIL
 
-  [AudioContext interface: attribute baseLatency]
-    expected: FAIL
-
   [AudioParam interface: new AudioBufferSourceNode(context).playbackRate must inherit property "cancelAndHoldAtTime(double)" with the proper type]
     expected: FAIL
 
-  [AudioContext interface: attribute outputLatency]
-    expected: FAIL
-
   [AudioListener interface: attribute upX]
     expected: FAIL
 

testing/web-platform/meta/webaudio/the-audio-api/the-audiocontext-interface/audiocontextoptions.html.ini

@@ -1,16 +1,4 @@
 [audiocontextoptions.html]
-  [X default baseLatency is not greater than 0. Got undefined.]
-    expected: FAIL
-
-  [X balanced baseLatency is not greater than or equal to undefined. Got undefined.]
-    expected: FAIL
-
-  [X playback baseLatency is not greater than or equal to undefined. Got undefined.]
-    expected: FAIL
-
-  [< [test-audiocontextoptions-latencyHint-basic\] 3 out of 9 assertions were failed.]
-    expected: FAIL
-
   [X double-constructor baseLatency small is not less than or equal to undefined. Got undefined.]
     expected: FAIL
 

testing/web-platform/tests/webaudio/the-audio-api/the-audiocontext-interface/audiocontextoptions.html

@@ -35,7 +35,7 @@
               `context.sampleRate (${context.sampleRate} Hz)`).beGreaterThan(0);
 
             defaultLatency = context.baseLatency;
-            should(defaultLatency, 'default baseLatency').beGreaterThan(0);
+            should(defaultLatency, 'default baseLatency').beGreaterThanOrEqualTo(0);
 
             // Verify that an AudioContext can be created with the expected
             // latency types.
@@ -130,7 +130,7 @@
             should(context1.baseLatency, 'high latency context baseLatency')
                 .beEqualTo(context2.baseLatency);
             should(context1.baseLatency, 'high latency context baseLatency')
-                .beGreaterThan(interactiveLatency);
+                .beGreaterThanOrEqualTo(interactiveLatency);
             closingPromises.push(context1.close());
             closingPromises.push(context2.close());