Add support for setting OPUS header gain.

media/filters/opus_audio_decoder.cc

Index: media/filters/opus_audio_decoder.cc
diff --git a/media/filters/opus_audio_decoder.cc b/media/filters/opus_audio_decoder.cc
index e3567209f1a83063e484af89f9222bc693dbe445..6762c9bb6bacbf5e6365fea43770ab1244f355e7 100644
--- a/media/filters/opus_audio_decoder.cc
+++ b/media/filters/opus_audio_decoder.cc
@@ -24,8 +24,9 @@
 
 namespace media {
 
-static uint16 ReadLE16(const uint8* data, size_t data_size, int read_offset) {
-  uint16 value = 0;
+template <typename T>
+static T ReadLE16(const uint8* data, size_t data_size, int read_offset) {
+  T value = 0;
   DCHECK_LE(read_offset + sizeof(value), data_size);
   memcpy(&value, data + read_offset, sizeof(value));
   return base::ByteSwapToLE16(value);
@@ -157,6 +158,9 @@ static const int kOpusExtraDataChannelsOffset = 9;
 // Offset to the pre-skip value in the Opus extra data.
 static const int kOpusExtraDataSkipSamplesOffset = 10;
 
+// Offset to the gain value in the Opus extra data.
+static const int kOpusExtraDataGainOffset = 16;
+
 // Offset to the channel mapping byte in the Opus extra data.
 static const int kOpusExtraDataChannelMappingOffset = 18;
 
@@ -179,16 +183,18 @@ struct OpusExtraData {
         skip_samples(0),
         channel_mapping(0),
         num_streams(0),
-        num_coupled(0) {
+        num_coupled(0),
+        gain_db(0) {
     memcpy(stream_map,
            kDefaultOpusChannelLayout,
            kMaxChannelsWithDefaultLayout);
   }
   int channels;
-  int skip_samples;
+  uint16_t skip_samples;
   int channel_mapping;
   int num_streams;
   int num_coupled;
+  int16_t gain_db;
   uint8 stream_map[kMaxVorbisChannels];
 };
 
@@ -212,7 +218,9 @@ static bool ParseOpusExtraData(const uint8* data, int data_size,
   }
 
   extra_data->skip_samples =
-      ReadLE16(data, data_size, kOpusExtraDataSkipSamplesOffset);
+      ReadLE16<uint16_t>(data, data_size, kOpusExtraDataSkipSamplesOffset);
+  extra_data->gain_db =
+      ReadLE16<int16_t>(data, data_size, kOpusExtraDataGainOffset);

[acolwell GONE FROM CHROMIUM, 2013/12/16 21:37:08]

nit: How about just putting a static_cast<int16_t>() here instead of making
ReadLE16() a template. It seems like that would result in less code and avoid
the implicit casting that is going on in your template (ie there is no int16_t
version of ByteSwapToLE16).

[DaleCurtis, 2013/12/16 22:21:04]

Nice catch, I've reverted this in place of just using a static_cast. 

 
   extra_data->channel_mapping = *(data + kOpusExtraDataChannelMappingOffset);
 
@@ -502,6 +510,13 @@ bool OpusAudioDecoder::ConfigureDecoder() {
     return false;
   }
 
+  status = opus_multistream_decoder_ctl(
+      opus_decoder_, OPUS_SET_GAIN(opus_extra_data.gain_db));
+  if (status != OPUS_OK) {
+    DLOG(WARNING) << "Failed to set OPUS header gain.  status="
+                  << opus_strerror(status);

[acolwell GONE FROM CHROMIUM, 2013/12/16 21:37:08]

nit: Shouldn't we return false here since this is a sign of invalid content?

[DaleCurtis, 2013/12/16 22:21:04]

While the docs don't make it clear, errors will be returned when the gain value
is outside of [-32768, 32767].  The test files I have play fine, so I've made it
an error.

[vignesh, 2013/12/16 22:24:51]

We do strict checking on other fields (like codec_delay). So i think we should
be strict here as well and return false.

[DaleCurtis, 2013/12/16 22:28:02]

The bounds are int16_min -> int16_max, it's enforced by virtue of being an int16
type.

+  }
+
   channel_layout_ = config.channel_layout();
   samples_per_second_ = config.samples_per_second();
   output_timestamp_helper_.reset(