Fixing bug that 8bit PCM stream is gabbled

The CodecContext passed into FFmpegAudioDecoder by
the FFmpegDemuxer says the output samples are 16bits.
So we tell the audio renderer to create a 16bits
audio output stream. But after the decoder is allocated
by avcodec_find_codec, the sample bits information in
|codec_context_| is changed to 8bit! So we are feeding
16bits output stream with 8bits data.

The decoder should knows more about the actual output
format. So query the sample bits information after
the decoder is allocated.

Review URL: http://codereview.chromium.org/125027

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@18406 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 10 insertions, 8 deletions

diff --git a/media/filters/ffmpeg_audio_decoder.cc b/media/filters/ffmpeg_audio_decoder.cc
index 78e764e..0b27519 100644
--- a/media/filters/ffmpeg_audio_decoder.cc
+++ b/media/filters/ffmpeg_audio_decoder.cc
@@ -42,7 +42,16 @@ bool FFmpegAudioDecoder::OnInitialize(DemuxerStream* demuxer_stream) {
   DCHECK_GT(av_get_bits_per_sample_format(codec_context_->sample_fmt), 0);
   DCHECK_GT(codec_context_->sample_rate, 0);
 
-  // Set the media format.
+  // Grab the codec context from FFmpeg demuxer.
+  AVCodec* codec = avcodec_find_decoder(codec_context_->codec_id);
+  if (!codec || avcodec_open(codec_context_, codec) < 0) {
+    host_->Error(PIPELINE_ERROR_DECODE);
+    return false;
+  }
+
+  // When calling avcodec_find_decoder(), |codec_context_| might be altered by
+  // the decoder to give more accurate values of the output format of the
+  // decoder. So set the media format after a decoder is allocated.
   // TODO(hclam): Reuse the information provided by the demuxer for now, we may
   // need to wait until the first buffer is decoded to know the correct
   // information.
@@ -54,13 +63,6 @@ bool FFmpegAudioDecoder::OnInitialize(DemuxerStream* demuxer_stream) {
   media_format_.SetAsString(MediaFormat::kMimeType,
       mime_type::kUncompressedAudio);
 
-  // Grab the codec context from FFmpeg demuxer.
-  AVCodec* codec = avcodec_find_decoder(codec_context_->codec_id);
-  if (!codec || avcodec_open(codec_context_, codec) < 0) {
-    host_->Error(PIPELINE_ERROR_DECODE);
-    return false;
-  }
-
   // Prepare the output buffer.
   output_buffer_.reset(static_cast<uint8*>(av_malloc(kOutputBufferSize)));
   if (!output_buffer_.get()) {