[Chromoting] Implement down mixing in AudioPump

remoting/proto/audio.proto

Index: remoting/proto/audio.proto
diff --git a/remoting/proto/audio.proto b/remoting/proto/audio.proto
index f64daaed748a1492f3fc7999a017e68a4001006c..2b80669cf45a1ec36386238a5985f07e77d62d27 100644
--- a/remoting/proto/audio.proto
+++ b/remoting/proto/audio.proto
@@ -47,6 +47,12 @@ message AudioPacket {
     CHANNELS_INVALID = -1;
     CHANNELS_MONO = 1;
     CHANNELS_STEREO = 2;
+    CHANNELS_SURROUND = 3;

[tommi (sloooow) - chröme, 2017/06/08 17:58:07]

what about 2.1?

[Hzj_jie, 2017/06/08 19:07:48]

We do not support 2.1 for now: all 3 channels layout will be treated as
surround. Because we always downmix the audio to stereo. AFAICT, downmixing 2.1
or surround to stereo makes very limited differences here.

+    CHANNELS_4_0 = 4;
+    CHANNELS_4_1 = 5;
+    CHANNELS_5_1 = 6;
+    CHANNELS_6_1 = 7;
+    CHANNELS_7_1 = 8;
   }
 
   optional Channels channels = 6 [default = CHANNELS_INVALID];