Always use 48kHz for OPUS decoding.

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 267 matching lines @@
   DCHECK_EQ(codec_context->codec_type, AVMEDIA_TYPE_AUDIO);
 
   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);
 
+  int sample_rate = codec_context->sample_rate;
   if (codec == kCodecOpus) {
     // |codec_context->sample_fmt| is not set by FFmpeg because Opus decoding is
     // 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 = kSampleFormatF32;
+
+    // Always use 48kHz for OPUS.  Technically we should match to the highest
+    // supported hardware sample rate among [8, 12, 16, 24, 48] kHz, but we
+    // don't know the hardware sample rate at this point and those rates are
+    // rarely used for output.  See the "Input Sample Rate" section of the spec:
+    // http://tools.ietf.org/html/draft-terriberry-oggopus-01#page-11
+    sample_rate = 48000;
   }
 
   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);
   }
 
   config->Initialize(codec,
                      sample_format,
                      channel_layout,
-                     codec_context->sample_rate,
+                     sample_rate,
                      codec_context->extradata,
                      codec_context->extradata_size,
                      is_encrypted,
                      record_stats,
                      seek_preroll,
                      codec_context->delay);
   if (codec != kCodecOpus) {
     DCHECK_EQ(av_get_bytes_per_sample(codec_context->sample_fmt) * 8,
               config->bits_per_channel());
   }
@@ skipping 263 matching lines @@
       return false;
 
     *out = parsed_time;
     return true;
   }
 
   return false;
 }
 
 }  // namespace media