Cleanup OPUS decoder. Remove extraneous transforms and copies.

media/ffmpeg/ffmpeg_common.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/ffmpeg/ffmpeg_common.h"
 
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 268 matching lines @@
   AudioCodec codec = CodecIDToAudioCodec(codec_context->codec_id);
 
   SampleFormat sample_format =
       AVSampleFormatToSampleFormat(codec_context->sample_fmt);
 
   ChannelLayout channel_layout = ChannelLayoutToChromeChannelLayout(
       codec_context->channel_layout, codec_context->channels);
 
   if (codec == kCodecOpus) {
     // |codec_context->sample_fmt| is not set by FFmpeg because Opus decoding is
-    // not enabled in FFmpeg, so we need to manually set the sample format.
+    // not enabled in FFmpeg.  It doesn't matter what value is set here, so long
+    // as it's valid, the true sample format is selected inside the decoder.
     sample_format = kSampleFormatS16;
   }
 
   base::TimeDelta seek_preroll;
   if (codec_context->seek_preroll > 0) {
     seek_preroll = base::TimeDelta::FromMicroseconds(
         codec_context->seek_preroll * 1000000.0 / codec_context->sample_rate);
   }
 
   base::TimeDelta codec_delay;
@@ skipping 235 matching lines @@
       return PIX_FMT_YUVJ420P;
     case VideoFrame::YV12A:
       return PIX_FMT_YUVA420P;
     default:
       DVLOG(1) << "Unsupported VideoFrame::Format: " << video_format;
   }
   return PIX_FMT_NONE;
 }
 
 }  // namespace media