Feed the WebRTC APM with empty far-end frames for the number of frames skipped by OS.

content/renderer/media/media_stream_audio_processor.cc

Index: content/renderer/media/media_stream_audio_processor.cc
diff --git a/content/renderer/media/media_stream_audio_processor.cc b/content/renderer/media/media_stream_audio_processor.cc
index 5e4c1c0569d0c01044246d82c01ab07a12b74392..b3ae7c6efcc762b4d407ebb0e91f0f18d8409242 100644
--- a/content/renderer/media/media_stream_audio_processor.cc
+++ b/content/renderer/media/media_stream_audio_processor.cc
@@ -279,7 +279,8 @@ MediaStreamAudioProcessor::MediaStreamAudioProcessor(
       playout_data_source_(playout_data_source),
       audio_mirroring_(false),
       typing_detected_(false),
-      stopped_(false) {
+      stopped_(false),
+      skipped_output_frames_(0) {
   capture_thread_checker_.DetachFromThread();
   render_thread_checker_.DetachFromThread();
   InitializeAudioProcessingModule(constraints, input_params);
@@ -432,7 +433,8 @@ void MediaStreamAudioProcessor::OnIpcClosing() {
 
 void MediaStreamAudioProcessor::OnPlayoutData(media::AudioBus* audio_bus,
                                               int sample_rate,
-                                              int audio_delay_milliseconds) {
+                                              int audio_delay_milliseconds,
+                                              uint32_t skipped_frames) {
   DCHECK(render_thread_checker_.CalledOnValidThread());
   DCHECK(audio_processing_->echo_control_mobile()->is_enabled() ^
          audio_processing_->echo_cancellation()->is_enabled());
@@ -447,6 +449,25 @@ void MediaStreamAudioProcessor::OnPlayoutData(media::AudioBus* audio_bus,
 
   render_fifo_->Push(
       *audio_bus, base::TimeDelta::FromMilliseconds(audio_delay_milliseconds));
+
+  // Feed the APM with empty frames if frames have been skipped. The APM only
+  // accepts 10 ms chunks.
+  skipped_output_frames_ += skipped_frames;
+  uint32_t frames_per_10ms = static_cast<uint32_t>(sample_rate / 100);
+  if (skipped_output_frames_ > frames_per_10ms) {
+    MediaStreamAudioBus empty_bus(audio_bus->channels(), frames_per_10ms);
+    empty_bus.bus()->Zero();
+    while (skipped_output_frames_ > frames_per_10ms) {
+      audio_processing_->AnalyzeReverseStream(
+          empty_bus.channel_ptrs(),
+          empty_bus.bus()->frames(),
+          sample_rate,
+          ChannelsToLayout(empty_bus.bus()->channels()));
+      skipped_output_frames_ -= frames_per_10ms;
+    }
+  }
+
+  // Pull data from the fifo and feed the APM.
   MediaStreamAudioBus* analysis_bus;
   base::TimeDelta audio_delay;
   while (render_fifo_->Consume(&analysis_bus, &audio_delay)) {
@@ -455,7 +476,7 @@ void MediaStreamAudioProcessor::OnPlayoutData(media::AudioBus* audio_bus,
         analysis_bus->channel_ptrs(),
         analysis_bus->bus()->frames(),
         sample_rate,
-        ChannelsToLayout(audio_bus->channels()));
+        ChannelsToLayout(analysis_bus->bus()->channels()));
   }
 }