Make sure that DecodeAudioFileData() always returns an AudioBus of the exact length of the file

BUG=none
TEST=extensive manual testing, two Web Audio layout tests for decoding need to be re-baselined
Review URL: https://codereview.chromium.org/11137005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@161914 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 19 insertions, 7 deletions

diff --git a/media/filters/audio_file_reader.cc b/media/filters/audio_file_reader.cc
index 628f951..eea0eed 100644
--- a/media/filters/audio_file_reader.cc
+++ b/media/filters/audio_file_reader.cc
@@ -35,7 +35,12 @@ int AudioFileReader::sample_rate() const {
 
 base::TimeDelta AudioFileReader::duration() const {
   const AVRational av_time_base = {1, AV_TIME_BASE};
-  return ConvertFromTimeBase(av_time_base, format_context_->duration);
+
+  // Add one microsecond to avoid rounding-down errors which can occur when
+  // |duration| has been calculated from an exact number of sample-frames.
+  // One microsecond is much less than the time of a single sample-frame
+  // at any real-world sample-rate.
+  return ConvertFromTimeBase(av_time_base, format_context_->duration + 1);
 }
 
 int64 AudioFileReader::number_of_frames() const {
@@ -110,13 +115,13 @@ void AudioFileReader::Close() {
   }
 }
 
-bool AudioFileReader::Read(AudioBus* audio_bus) {
+int AudioFileReader::Read(AudioBus* audio_bus) {
   DCHECK(format_context_ && codec_context_) <<
       "AudioFileReader::Read() : reader is not opened!";
 
   DCHECK_EQ(audio_bus->channels(), channels());
   if (audio_bus->channels() != channels())
-    return false;
+    return 0;
 
   size_t bytes_per_sample = av_get_bytes_per_sample(codec_context_->sample_fmt);
 
@@ -187,8 +192,9 @@ bool AudioFileReader::Read(AudioBus* audio_bus) {
   audio_bus->ZeroFramesPartial(
       current_frame, audio_bus->frames() - current_frame);
 
-  // Fail if nothing has been decoded, otherwise return partial data.
-  return current_frame > 0;
+  // Returns the actual number of sample-frames decoded.
+  // Ideally this represents the "true" exact length of the file.
+  return current_frame;
 }
 
 }  // namespace media
diff --git a/media/filters/audio_file_reader.h b/media/filters/audio_file_reader.h
index b8f54b6..726ab7d 100644
--- a/media/filters/audio_file_reader.h
+++ b/media/filters/audio_file_reader.h
@@ -37,12 +37,18 @@ class MEDIA_EXPORT AudioFileReader {
   // |audio_data| must be of the same size as channels().
   // The audio data will be decoded as floating-point linear PCM with
   // a nominal range of -1.0 -> +1.0.
-  // Returns |true| on success.
-  bool Read(AudioBus* audio_bus);
+  // Returns the number of sample-frames actually read which will always be
+  // <= audio_bus->frames()
+  int Read(AudioBus* audio_bus);
 
   // These methods can be called once Open() has been called.
   int channels() const;
   int sample_rate() const;
+
+  // Please note that duration() and number_of_frames() attempt to be accurate,
+  // but are only estimates.  For some encoded formats, the actual duration
+  // of the file can only be determined once all the file data has been read.
+  // The Read() method returns the actual number of sample-frames it has read.
   base::TimeDelta duration() const;
   int64 number_of_frames() const;