Forward the number of skipped frames by the OS in audio playout.

* Only for Mac.

Will be done in follow-up CLs:
* Windows.
* Hooking this up to the AEC.

BUG=560371

Review URL: https://codereview.chromium.org/1487983002

Cr-Commit-Position: refs/heads/master@{#364990}

1 files changed, 17 insertions, 3 deletions

diff --git a/content/browser/renderer_host/media/audio_sync_reader.cc b/content/browser/renderer_host/media/audio_sync_reader.cc
index f6b3d6c..ea794a2 100644
--- a/content/browser/renderer_host/media/audio_sync_reader.cc
+++ b/content/browser/renderer_host/media/audio_sync_reader.cc
@@ -15,6 +15,7 @@
 #include "media/audio/audio_parameters.h"
 
 using media::AudioBus;
+using media::AudioOutputBuffer;
 
 namespace {
 
@@ -51,8 +52,12 @@ AudioSyncReader::AudioSyncReader(base::SharedMemory* shared_memory,
       maximum_wait_time_(base::TimeDelta::FromMilliseconds(20)),
 #endif
       buffer_index_(0) {
-  DCHECK_EQ(packet_size_, AudioBus::CalculateMemorySize(params));
-  output_bus_ = AudioBus::WrapMemory(params, shared_memory->memory());
+  DCHECK_EQ(static_cast<size_t>(packet_size_),
+            sizeof(media::AudioOutputBufferParameters) +
+                AudioBus::CalculateMemorySize(params));
+  AudioOutputBuffer* buffer =
+      reinterpret_cast<AudioOutputBuffer*>(shared_memory_->memory());
+  output_bus_ = AudioBus::WrapMemory(params, buffer->audio);
   output_bus_->Zero();
 }
 
@@ -81,10 +86,19 @@ AudioSyncReader::~AudioSyncReader() {
 }
 
 // media::AudioOutputController::SyncReader implementations.
-void AudioSyncReader::UpdatePendingBytes(uint32 bytes) {
+void AudioSyncReader::UpdatePendingBytes(uint32_t bytes,
+                                         uint32_t frames_skipped) {
+  // Increase the number of skipped frames stored in shared memory. We don't
+  // send it over the socket since sending more than 4 bytes might lead to being
+  // descheduled. The reading side will zero it when consumed.
+  AudioOutputBuffer* buffer =
+      reinterpret_cast<AudioOutputBuffer*>(shared_memory_->memory());
+  buffer->params.frames_skipped += frames_skipped;
+
   // Zero out the entire output buffer to avoid stuttering/repeating-buffers
   // in the anomalous case if the renderer is unable to keep up with real-time.
   output_bus_->Zero();
+
   socket_->Send(&bytes, sizeof(bytes));
   ++buffer_index_;
 }