Implementation of 'AudioContext.getOutputTimestamp' method

media/audio/win/audio_low_latency_output_win.cc

Index: media/audio/win/audio_low_latency_output_win.cc
diff --git a/media/audio/win/audio_low_latency_output_win.cc b/media/audio/win/audio_low_latency_output_win.cc
index 9fa035d80ba6aec06859dfcea5c2f04202e0e1cd..d55a0bcca410277470af43c482acd9562fc7f20d 100644
--- a/media/audio/win/audio_low_latency_output_win.cc
+++ b/media/audio/win/audio_low_latency_output_win.cc
@@ -71,6 +71,7 @@ WASAPIAudioOutputStream::WASAPIAudioOutputStream(AudioManagerWin* manager,
       share_mode_(GetShareMode()),
       num_written_frames_(0),
       source_(NULL),
+      hns_units_to_perf_count_(0.0),
       audio_bus_(AudioBus::Create(params)) {
   DCHECK(manager_);
 
@@ -127,6 +128,14 @@ WASAPIAudioOutputStream::WASAPIAudioOutputStream(AudioManagerWin* manager,
   // Create the event which will be set in Stop() when capturing shall stop.
   stop_render_event_.Set(CreateEvent(NULL, FALSE, FALSE, NULL));
   DCHECK(stop_render_event_.IsValid());
+
+  LARGE_INTEGER performance_frequency;
+  if (QueryPerformanceFrequency(&performance_frequency)) {
+    hns_units_to_perf_count_ =
+        (static_cast<double>(performance_frequency.QuadPart) / 10000000.0);
+  } else {
+    DLOG(ERROR) << "High-resolution performance counters are not supported.";
+  }
 }
 
 WASAPIAudioOutputStream::~WASAPIAudioOutputStream() {
@@ -511,8 +520,11 @@ bool WASAPIAudioOutputStream::RenderAudioFromSource(UINT64 device_frequency) {
     // can typically be utilized by an acoustic echo-control (AEC)
     // unit at the render side.
     UINT64 position = 0;
+    UINT64 qpc_position = 0;

[Raymond Toy, 2016/06/14 16:42:40]

What does "qpc" stand for?  

[Mikhail, 2016/06/17 09:36:57]

that is 'QueryPerformanceCounter', renaming to 'performance_counter_position'

     uint32_t audio_delay_bytes = 0;
-    hr = audio_clock_->GetPosition(&position, NULL);
+    AudioTimestamp output_timestamp = {0, 0};
+
+    hr = audio_clock_->GetPosition(&position, &qpc_position);
     if (SUCCEEDED(hr)) {
       // Stream position of the sample that is currently playing
       // through the speaker.
@@ -529,13 +541,19 @@ bool WASAPIAudioOutputStream::RenderAudioFromSource(UINT64 device_frequency) {
       // render client using the OnMoreData() callback.
       audio_delay_bytes = (pos_last_sample_written_frames -
           pos_sample_playing_frames) *  format_.Format.nBlockAlign;
+      if (hns_units_to_perf_count_) {
+        output_timestamp.frames = pos_sample_playing_frames;
+        output_timestamp.ticks = base::TimeTicks::FromQPCValue(
+                                     qpc_position * hns_units_to_perf_count_)
+                                     .ToInternalValue();
+      }
     }
 
     // Read a data packet from the registered client source and
     // deliver a delay estimate in the same callback to the client.
 
-    int frames_filled =
-        source_->OnMoreData(audio_bus_.get(), audio_delay_bytes, 0);
+    int frames_filled = source_->OnMoreData(audio_bus_.get(), audio_delay_bytes,
+                                            0, output_timestamp);
     uint32_t num_filled_bytes = frames_filled * format_.Format.nBlockAlign;
     DCHECK_LE(num_filled_bytes, packet_size_bytes_);