[Chromecast] Process streams with different post-processing.

chromecast/media/cma/backend/alsa/stream_mixer_alsa.h

Index: chromecast/media/cma/backend/alsa/stream_mixer_alsa.h
diff --git a/chromecast/media/cma/backend/alsa/stream_mixer_alsa.h b/chromecast/media/cma/backend/alsa/stream_mixer_alsa.h
index 53a48911f72ae92fe6fed42b1db7703d52aab2fd..80f7658cca985b4b86ef666d04e06faf37668dbf 100644
--- a/chromecast/media/cma/backend/alsa/stream_mixer_alsa.h
+++ b/chromecast/media/cma/backend/alsa/stream_mixer_alsa.h
@@ -29,6 +29,8 @@ namespace chromecast {
 namespace media {
 class AlsaWrapper;
 
+const int kNumFilterGroups = 2;
+
 // Mixer implementation. The mixer has one or more input queues; these can be
 // added/removed at any time. When an input source pushes frames to an input
 // queue, the queue should call StreamMixerAlsa::WriteFrames(); this causes
@@ -38,7 +40,28 @@ class AlsaWrapper;
 // uses the minimum value). Assuming that all primary inputs have some data
 // available, the calculated number of frames are pulled from each input (maybe
 // resampled, if the input's incoming sample rate is not equal to the mixer's
-// output sample rate) and written to the ALSA stack.
+// output sample rate), mixed and written to the ALSA stack.
+//
+// MIXER ARCHITECTURE
+// The mixer allows multiple streams to be grouped together for post-processing
+// purposes. Each group has a single AudioFilterInterface instance that
+// is used to post-process the data before a final mixing stage.
+//
+//  Stream  Stream  Stream   Stream  Stream   <- Input streams
+//    |        |       |       |       |
+//  ---------------------   ----------------
+//  |  Media Mixer      |   | System Mixer |  <- Intermediate mix
+//  ---------------------   ----------------
+//           |                     |
+//  ---------------------   -----------------
+//  |  Media Filter     |   | System Filter |
+//  ---------------------   -----------------
+//                 \             /
+//                -----------------
+//                |  Final Mixer  |
+//                -----------------
+//                        |
+//                      ALSA
 //
 // The rendering delay is recalculated after every successful write to the ALSA
 // stack. This delay is passed up to the input sources whenever some new data
@@ -67,6 +90,11 @@ class StreamMixerAlsa {
     // precedence for sample rates and will dictate when data is polled.
     virtual bool primary() const = 0;
 
+    // Returns a string describing the content type class.
+    // Should be from chromecast/public/media/audio_device_ids.h
+    // or media/audio/audio_device_description.h
+    virtual std::string name() const = 0;
+
     // Returns true if PrepareToDelete() has been called.
     virtual bool IsDeleting() const = 0;
 
@@ -195,10 +223,20 @@ class StreamMixerAlsa {
 
   void WriteFrames();
   bool TryWriteFrames();
-  void WriteMixedPcm(const ::media::AudioBus& mixed, int frames,
-      bool is_silence);
+
+  // Mixes |active_inputs| and processes the resulting buffer
+  // with pre_loopback_filter_[|filter|].
+  // If |accumulate| is false, |interleaved_| will be overwritten
+  //  (rather than summed).
+  // Returns |true| if non-zero data was written to |interleaved_|.
+  bool MixAndFilterGroup(const std::vector<InputQueue*>& active_inputs,
+                         int filter,
+                         int frames,
+                         bool accumulate);
+  void WriteMixedPcm(int frames);
   void UpdateRenderingDelay(int newly_pushed_frames);
   ssize_t BytesPerOutputFormatSample();
+  void ResizeBuffersIfNecessary(int chunk_size);
 
   static bool single_threaded_for_test_;
 
@@ -229,6 +267,8 @@ class StreamMixerAlsa {
   std::vector<std::unique_ptr<InputQueue>> inputs_;
   std::vector<std::unique_ptr<InputQueue>> ignored_inputs_;
   MediaPipelineBackendAlsa::RenderingDelay rendering_delay_;
+  // Buffer to write intermediate mixes during post-processing.
+  std::vector<uint8_t> interleaved_intermediate_;
   // Buffer to write final interleaved data before sending to snd_pcm_writei().
   std::vector<uint8_t> interleaved_;
 
@@ -245,9 +285,8 @@ class StreamMixerAlsa {
 
   std::vector<CastMediaShlib::LoopbackAudioObserver*> loopback_observers_;
 
-  std::unique_ptr<AudioFilterInterface> pre_loopback_filter_;
-  std::unique_ptr<AudioFilterInterface> post_loopback_filter_;
-  int silence_frames_filtered_ = 0;
+  std::unique_ptr<AudioFilterInterface> pre_loopback_filter_[kNumFilterGroups];

[tianyuwang1, 2017/02/18 00:17:08]

Since there's no post_loopback_filter_ anymore, just call this output_filter or
playout_filter?  

[bshaya, 2017/02/21 23:30:14]

Done.

+  int silence_frames_filtered_[kNumFilterGroups];
 
   DISALLOW_COPY_AND_ASSIGN(StreamMixerAlsa);
 };