Support (E)AC3 passthrough

media/base/audio_renderer_mixer.cc

Index: media/base/audio_renderer_mixer.cc
diff --git a/media/base/audio_renderer_mixer.cc b/media/base/audio_renderer_mixer.cc
index b61a04a766eec5504206e05994566473f9e12a60..386703e748211788b7186226ab76accf3afb3ae9 100644
--- a/media/base/audio_renderer_mixer.cc
+++ b/media/base/audio_renderer_mixer.cc
@@ -54,6 +54,7 @@ AudioRendererMixer::AudioRendererMixer(const AudioParameters& output_params,
                                        const UmaLogCallback& log_callback)
     : output_params_(output_params),
       audio_sink_(std::move(sink)),
+      raw_input_(nullptr),

[DaleCurtis, 2016/11/01 23:05:13]

Why is this necessary? Instead the AudioConverter should be taught about raw
streams and it will do the right thing without modification to this code.

[AndyWu, 2016/11/04 18:04:24]

Just took a shortcut, since none of these functions are applicable to raw
stream.
I will look into AudioConverter.

[AndyWu, 2016/11/04 19:43:48]

You are right, the change is not necessary.

       master_converter_(output_params, output_params, true),
       pause_delay_(base::TimeDelta::FromSeconds(kPauseDelaySeconds)),
       last_play_time_(base::TimeTicks::Now()),
@@ -84,6 +85,14 @@ void AudioRendererMixer::AddMixerInput(const AudioParameters& input_params,
     audio_sink_->Play();
   }
 
+  if (input_params.IsRawFormat()) {
+    DCHECK(input);
+    DCHECK(!raw_input_);
+
+    raw_input_ = input;
+    return;
+  }
+
   int input_sample_rate = input_params.sample_rate();
   if (is_master_sample_rate(input_sample_rate)) {
     master_converter_.AddInput(input);
@@ -115,6 +124,11 @@ void AudioRendererMixer::RemoveMixerInput(
     AudioConverter::InputCallback* input) {
   base::AutoLock auto_lock(lock_);
 
+  if (raw_input_ == input) {
+    raw_input_ = nullptr;
+    return;
+  }
+
   int input_sample_rate = input_params.sample_rate();
   if (is_master_sample_rate(input_sample_rate)) {
     master_converter_.RemoveInput(input);
@@ -168,6 +182,10 @@ int AudioRendererMixer::Render(AudioBus* audio_bus,
   TRACE_EVENT0("audio", "AudioRendererMixer::Render");
   base::AutoLock auto_lock(lock_);
 
+  if (raw_input_) {
+    return raw_input_->ProvideInput(audio_bus, frames_delayed);
+  }
+
   // If there are no mixer inputs and we haven't seen one for a while, pause the
   // sink to avoid wasting resources when media elements are present but remain
   // in the pause state.