Rewriting FFmpegAudioDecoder and eliminating DecoderBase.

media/filters/ffmpeg_audio_decoder.cc

Index: media/filters/ffmpeg_audio_decoder.cc
diff --git a/media/filters/ffmpeg_audio_decoder.cc b/media/filters/ffmpeg_audio_decoder.cc
index 807f1d16002f43da1b0771c7023dc0f3f8339a89..367ba095f3bf246b8ecd0107642111c9518d8d6b 100644
--- a/media/filters/ffmpeg_audio_decoder.cc
+++ b/media/filters/ffmpeg_audio_decoder.cc
@@ -4,68 +4,149 @@
 
 #include "media/filters/ffmpeg_audio_decoder.h"
 
-#include "media/base/callback.h"
-#include "media/base/data_buffer.h"
+#include "media/base/filter_host.h"
 #include "media/base/limits.h"
 #include "media/ffmpeg/ffmpeg_common.h"
-#include "media/filters/ffmpeg_demuxer.h"
-
-#if !defined(USE_SSE)
-#if defined(__SSE__) || defined(ARCH_CPU_X86_64) || _M_IX86_FP==1
-#define USE_SSE 1
-#else
-#define USE_SSE 0
-#endif
-#endif
-#if USE_SSE
-#include <xmmintrin.h>
-#endif
 
 namespace media {
 
-// Size of the decoded audio buffer.
-const size_t FFmpegAudioDecoder::kOutputBufferSize =
-    AVCODEC_MAX_AUDIO_FRAME_SIZE;
+static bool IsErrorResult(int result, int decoded_size) {
+  return result < 0 ||
+      decoded_size < 0 ||
+      decoded_size > AVCODEC_MAX_AUDIO_FRAME_SIZE;
+}
+
+static bool ProducedAudioSamples(int decoded_size) {
+  return decoded_size != 0;

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

do we want this to return true if decoded_size < 0?

[scherkus (not reviewing), 2011/09/11 14:49:22]

Hmm... yeah these helper methods are a bit weird since they're called in order
but I agree I'll make them more robust to calling order (generally a good thing)

+}
+
+static bool IsTimestampMarkerPacket(int result, Buffer* input) {
+  // We can get a positive result but no decoded data.  This is ok because this
+  // this can be a marker packet that only contains timestamp.
+  return result && !input->IsEndOfStream() &&

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

It's ok if result < 0? Perhaps a comment indicating what result represents would
be helpful.

[scherkus (not reviewing), 2011/09/11 14:49:22]

Done.

+      input->GetTimestamp() != kNoTimestamp &&
+      input->GetDuration() != kNoTimestamp;
+}
+
+static bool IsEndOfStream(int result, int decoded_size, Buffer* input) {
+  // Three conditions to meet to declare end of stream for this decoder:
+  // 1. FFmpeg didn't read anything.
+  // 2. FFmpeg didn't output anything.
+  // 3. An end of stream buffer is received.
+  return result == 0 && decoded_size == 0 && input->IsEndOfStream();

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

result -> read_size?

+}
 
 FFmpegAudioDecoder::FFmpegAudioDecoder(MessageLoop* message_loop)
-    : DecoderBase<AudioDecoder, Buffer>(message_loop),
+    : message_loop_(message_loop),
+      demuxer_stream_(NULL),
       codec_context_(NULL),
       config_(0, 0, 0),
-      estimated_next_timestamp_(kNoTimestamp) {
+      estimated_next_timestamp_(kNoTimestamp),
+      pending_reads_(0) {
 }
 
 FFmpegAudioDecoder::~FFmpegAudioDecoder() {
+  if (codec_context_) {

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

nit:braces not necesssary

[scherkus (not reviewing), 2011/09/11 14:49:22]

Done.

+    avcodec_close(codec_context_);
+  }
 }
 
-void FFmpegAudioDecoder::DoInitialize(DemuxerStream* demuxer_stream,
-                                      bool* success,
-                                      Task* done_cb) {
-  AutoTaskRunner done_runner(done_cb);
-  *success = false;
+void FFmpegAudioDecoder::Play(FilterCallback* callback) {

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

remove

[scherkus (not reviewing), 2011/09/11 14:49:22]

Done.

+  // XXX: anything else?
+  callback->Run();
+  delete callback;
+}
 
-  AVStream* av_stream = demuxer_stream->GetAVStream();
-  if (!av_stream) {
-    return;
-  }
+void FFmpegAudioDecoder::Pause(FilterCallback* callback) {

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

remove

[scherkus (not reviewing), 2011/09/11 14:49:22]

Done.

+  // XXX: anything else?
+  callback->Run();
+  delete callback;
+}
+
+void FFmpegAudioDecoder::Flush(FilterCallback* callback) {
+  // XXX: move to proper thread.

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

Or you could just protect this with a lock?

[scherkus (not reviewing), 2011/09/11 14:49:22]

Done.

+  avcodec_flush_buffers(codec_context_);
+  estimated_next_timestamp_ = kNoTimestamp;
+
+  callback->Run();
+  delete callback;
+}
+
+void FFmpegAudioDecoder::Stop(FilterCallback* callback) {
+  // XXX: anything else?

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

Clear consume callback so we won't send any data downstream? Keep track of
stopped state so we don't call Read() on DemuxerStream?

+  callback->Run();
+  delete callback;
+}
+
+void FFmpegAudioDecoder::Seek(base::TimeDelta time, FilterCallback* callback) {

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

remove

[scherkus (not reviewing), 2011/09/11 14:49:22]

Done.

+  // XXX: anything else?
+  callback->Run();
+  delete callback;
+}
+
+void FFmpegAudioDecoder::Initialize(
+    DemuxerStream* stream,
+    FilterCallback* callback,
+    StatisticsCallback* stats_callback) {
+  // XXX: do we still care about initializing on our own message_loop_?

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

I'm fine with keeping a message_loop for audio decoding.

+  // XXX: do we want to try and use MessageLoopProxy at this time?

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

separate CL IMO

+  // TODO(scherkus): change Initialize() signature to pass |stream| as a
+  // scoped_refptr<>.
+  scoped_refptr<DemuxerStream> ref_stream(stream);
+  message_loop_->PostTask(
+      FROM_HERE,
+      NewRunnableMethod(this, &FFmpegAudioDecoder::DoInitialize,
+                        ref_stream, callback, stats_callback));
+}
+
+AudioDecoderConfig FFmpegAudioDecoder::config() {
+  return config_;
+}
+
+void FFmpegAudioDecoder::ProduceAudioSamples(scoped_refptr<Buffer> buffer) {
+  message_loop_->PostTask(

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

What about just putting this in an  "if(MessageLoop::current() ==
message_loop_)" guard here and combine ProduceAudioSamples &
DoQueueOutputBuffer?

[scherkus (not reviewing), 2011/09/11 14:49:22]

I prefer the extra methods for clarity and saner debugging

+      FROM_HERE,
+      NewRunnableMethod(this, &FFmpegAudioDecoder::DoQueueOutputBuffer,
+                        buffer));
+}
 
-  // Grab the AVStream's codec context and make sure we have sensible values.
-  codec_context_ = av_stream->codec;
-  int bps = av_get_bits_per_sample_fmt(codec_context_->sample_fmt);
-  if (codec_context_->channels <= 0 ||
-      codec_context_->channels > Limits::kMaxChannels ||
-      bps <= 0 || bps > Limits::kMaxBitsPerSample ||
-      codec_context_->sample_rate <= 0 ||
-      codec_context_->sample_rate > Limits::kMaxSampleRate) {
-    DLOG(WARNING) << "Invalid audio stream -"
-        << " channels: " << codec_context_->channels
-        << " bps: " << bps
-        << " sample rate: " << codec_context_->sample_rate;
+void FFmpegAudioDecoder::DoInitialize(
+    DemuxerStream* stream,

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

consider moving this to Initialize() and using an  "if(MessageLoop::current() ==
message_loop_)" guard.

+    FilterCallback* callback,
+    StatisticsCallback* stats_callback) {
+  scoped_ptr<FilterCallback> c(callback);
+
+  demuxer_stream_ = stream;
+  AVStream* av_stream = demuxer_stream_->GetAVStream();
+  CHECK(av_stream);
+
+  stats_callback_.reset(stats_callback);
+
+  // Sanity checks.
+  AVCodecContext* codec_context = av_stream->codec;
+  if (!codec_context ||
+      codec_context->channels <= 0 ||
+      codec_context->channels > Limits::kMaxChannels ||
+      codec_context->sample_rate <= 0 ||
+      codec_context->sample_rate > Limits::kMaxSampleRate) {
+    DLOG(ERROR) << "Invalid audio format ("
+                << " channels: " << codec_context->channels
+                << " sample rate: " << codec_context->sample_rate << ")";
+
+    // XXX: should this be a "format" error?
+    host()->SetError(PIPELINE_ERROR_DECODE);
+    callback->Run();
     return;
   }
 
-  // Serialize calls to avcodec_open().
-  AVCodec* codec = avcodec_find_decoder(codec_context_->codec_id);
-  if (!codec || avcodec_open(codec_context_, codec) < 0) {
+  AVCodec* codec = avcodec_find_decoder(codec_context->codec_id);
+  if (!codec) {
+    DLOG(ERROR) << "Audio codec not found ("
+                << " codec_id: " << codec_context->codec_id << ")";
+
+    // XXX: should this be a "format" error?
+    host()->SetError(PIPELINE_ERROR_DECODE);
+    callback->Run();

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

Would this be a good time to convert Initialize() to use FilterStatusCB?

[scherkus (not reviewing), 2011/09/11 14:49:22]

Follow up CL

     return;
   }
 
@@ -74,185 +155,163 @@ void FFmpegAudioDecoder::DoInitialize(DemuxerStream* demuxer_stream,
   config_.channels_per_sample = codec_context_->channels;
   config_.sample_rate = codec_context_->sample_rate;
 
-  // Prepare the output buffer.
-  output_buffer_.reset(static_cast<uint8*>(av_malloc(kOutputBufferSize)));
-  if (!output_buffer_.get()) {
-    host()->SetError(PIPELINE_ERROR_OUT_OF_MEMORY);
+  // Prep our own AVCodecContext struct.
+  codec_context_ = avcodec_alloc_context();
+  codec_context_->channels = codec_context->channels;
+  codec_context_->sample_rate = codec_context->sample_rate;
+  codec_context_->sample_fmt = codec_context->sample_fmt;
+
+  if (avcodec_open(codec_context_, codec) < 0) {
+    DLOG(ERROR) << "Could not initialize audio decoder ("
+                << " codec_id: " << codec_context->codec_id
+                << " channels: " << codec_context->channels
+                << " sample rate: " << codec_context->sample_rate << ")";
+
+    // XXX: should this be a "format" error?
+    host()->SetError(PIPELINE_ERROR_DECODE);
+    callback->Run();
     return;
   }
-  *success = true;
-}
-
-AudioDecoderConfig FFmpegAudioDecoder::config() {
-  return config_;
-}
 
-void FFmpegAudioDecoder::ProduceAudioSamples(scoped_refptr<Buffer> output) {
-  DecoderBase<AudioDecoder, Buffer>::PostReadTaskHack(output);
-}
+  // XXX: the div-by-2 scares me a tiny bit for some reason.
+  decoded_audio_.reset(new int16_t[AVCODEC_MAX_AUDIO_FRAME_SIZE / 2]);

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

AVCODEC_MAX_AUDIO_FRAME_SIZE in bytes. We're allocating int16. We could just
have decoded_audio_ be uint8.

[scherkus (not reviewing), 2011/09/11 14:49:22]

Done and we'll do a reinterpret_cast<> in decode call

 
-void FFmpegAudioDecoder::DoSeek(base::TimeDelta time, Task* done_cb) {
-  avcodec_flush_buffers(codec_context_);
-  estimated_next_timestamp_ = kNoTimestamp;
-  done_cb->Run();
-  delete done_cb;
+  callback->Run();
 }
 
-// ConvertAudioF32ToS32() converts float audio (F32) to int (S32) in place.
-// This is a temporary solution.
-// The purpose of this short term fix is to enable WMApro, which decodes to
-// float.
-// The audio driver has been tested by passing the float audio thru.
-// FFmpeg for ChromeOS only exposes U8, S16 and F32.
-// To properly expose new audio sample types at the audio driver layer, a enum
-// should be created to represent all suppported types, including types
-// for Pepper.  FFmpeg should be queried for type and passed along.
-
-// TODO(fbarchard): Remove this function.  Expose all FFmpeg types to driver.
-// TODO(fbarchard): If this function is kept, move it to audio_util.cc
-
-#if USE_SSE
-const __m128 kFloatScaler = _mm_set1_ps( 2147483648.0f );
-static void FloatToIntSaturate(float* p) {
-  __m128 a = _mm_set1_ps(*p);
-  a = _mm_mul_ss(a, kFloatScaler);
-  *reinterpret_cast<int32*>(p) = _mm_cvtss_si32(a);
-}
-#else
-const float kFloatScaler = 2147483648.0f;
-const int kMinSample = std::numeric_limits<int32>::min();
-const int kMaxSample = std::numeric_limits<int32>::max();
-const float kMinSampleFloat =
-    static_cast<float>(std::numeric_limits<int32>::min());
-const float kMaxSampleFloat =
-    static_cast<float>(std::numeric_limits<int32>::max());
-static void FloatToIntSaturate(float* p) {
-  float f = *p * kFloatScaler + 0.5f;
-  int sample;
-  if (f <= kMinSampleFloat) {
-    sample = kMinSample;
-  } else if (f >= kMaxSampleFloat) {
-    sample = kMaxSample;
-  } else {
-    sample = static_cast<int32>(f);
-  }
-  *reinterpret_cast<int32*>(p) = sample;
-}
-#endif
-static void ConvertAudioF32ToS32(void* buffer, int buffer_size) {
-  for (int i = 0; i < buffer_size / 4; ++i) {
-    FloatToIntSaturate(reinterpret_cast<float*>(buffer) + i);
-  }
+void FFmpegAudioDecoder::DoQueueOutputBuffer(scoped_refptr<Buffer> output) {
+  output_buffers_.push_back(output);
+  ReadFromDemuxerStream();
 }
 
-void FFmpegAudioDecoder::DoDecode(Buffer* input) {
-  PipelineStatistics statistics;
+void FFmpegAudioDecoder::DoDecodeInputBuffer(scoped_refptr<Buffer> input) {
+  DCHECK(!output_buffers_.empty());
+  DCHECK_GT(pending_reads_, 0);
+  pending_reads_--;
 
   // FFmpeg tends to seek Ogg audio streams in the middle of nowhere, giving us
   // a whole bunch of AV_NOPTS_VALUE packets.  Discard them until we find
   // something valid.  Refer to http://crbug.com/49709
-  // TODO(hclam): remove this once fixing the issue in FFmpeg.
   if (input->GetTimestamp() == kNoTimestamp &&
       estimated_next_timestamp_ == kNoTimestamp &&
       !input->IsEndOfStream()) {
-    DecoderBase<AudioDecoder, Buffer>::OnDecodeComplete(statistics);
+    ReadFromDemuxerStream();
     return;
   }
 
-  // Due to FFmpeg API changes we no longer have const read-only pointers.
   AVPacket packet;
   av_init_packet(&packet);
   packet.data = const_cast<uint8*>(input->GetData());
   packet.size = input->GetDataSize();
 
+  PipelineStatistics statistics;
   statistics.audio_bytes_decoded = input->GetDataSize();
 
-  int16_t* output_buffer = reinterpret_cast<int16_t*>(output_buffer_.get());
-  int output_buffer_size = kOutputBufferSize;
+  int decoded_audio_size = AVCODEC_MAX_AUDIO_FRAME_SIZE;

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

This should be based on the size allocated. Perhaps introduce
decoded_audio_size_ member variable so that decode_audio_'s allocated size can't
get out of sync with this code.

[scherkus (not reviewing), 2011/09/11 14:49:22]

Done.

   int result = avcodec_decode_audio3(codec_context_,
-                                     output_buffer,
-                                     &output_buffer_size,
+                                     decoded_audio_.get(),
+                                     &decoded_audio_size,
                                      &packet);
 
+  // XXX: this is only for WMAPro audio codec?! remove?!

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

I'm fine with removing this since I don't think we want to encourage WMAPro
usage.

[scherkus (not reviewing), 2011/09/11 14:49:22]

Done.

+#if 0
   if (codec_context_->sample_fmt == SAMPLE_FMT_FLT) {
-    ConvertAudioF32ToS32(output_buffer, output_buffer_size);
+    ConvertAudioF32ToS32(decoded_audio_.get(), decoded_audio_size);
   }
+#endif
 
-  // TODO(ajwong): Consider if kOutputBufferSize should just be an int instead
-  // of a size_t.
-  if (result < 0 ||
-      output_buffer_size < 0 ||
-      static_cast<size_t>(output_buffer_size) > kOutputBufferSize) {
-    VLOG(1) << "Error decoding an audio frame with timestamp: "
-            << input->GetTimestamp().InMicroseconds() << " us, duration: "
-            << input->GetDuration().InMicroseconds() << " us, packet size: "
-            << input->GetDataSize() << " bytes";
-    DecoderBase<AudioDecoder, Buffer>::OnDecodeComplete(statistics);
+  if (IsErrorResult(result, decoded_audio_size)) {
+    DLOG(ERROR) << "Error decoding an audio frame with timestamp: "
+                << input->GetTimestamp().InMicroseconds() << " us, duration: "
+                << input->GetDuration().InMicroseconds() << " us, packet size: "
+                << input->GetDataSize() << " bytes";
+    ReadFromDemuxerStream();
     return;
   }
 
-  // If we have decoded something, enqueue the result.
-  if (output_buffer_size) {
-    DataBuffer* result_buffer = new DataBuffer(output_buffer_size);
-    result_buffer->SetDataSize(output_buffer_size);
-    uint8* data = result_buffer->GetWritableData();
-    memcpy(data, output_buffer, output_buffer_size);
-
-    // We don't trust the demuxer, so always calculate the duration based on
-    // the actual number of samples decoded.
-    base::TimeDelta duration = CalculateDuration(output_buffer_size);
-    result_buffer->SetDuration(duration);
-
-    // Use an estimated timestamp unless the incoming buffer has a valid one.
-    if (input->GetTimestamp() == kNoTimestamp) {
-      result_buffer->SetTimestamp(estimated_next_timestamp_);
-
-      // Keep the estimated timestamp invalid until we get an incoming buffer
-      // with a valid timestamp.  This can happen during seeks, etc...
-      if (estimated_next_timestamp_ != kNoTimestamp) {
-        estimated_next_timestamp_ += duration;
-      }
-    } else {
-      result_buffer->SetTimestamp(input->GetTimestamp());
-      estimated_next_timestamp_ = input->GetTimestamp() + duration;
-    }
-
-    EnqueueResult(result_buffer);
-    DecoderBase<AudioDecoder, Buffer>::OnDecodeComplete(statistics);
-    return;
-  }
+  scoped_refptr<DataBuffer> output;
 
-  // We can get a positive result but no decoded data.  This is ok because this
-  // this can be a marker packet that only contains timestamp.  In this case we
-  // save the timestamp for later use.
-  if (result && !input->IsEndOfStream() &&
-      input->GetTimestamp() != kNoTimestamp &&
-      input->GetDuration() != kNoTimestamp) {
+  if (ProducedAudioSamples(decoded_audio_size)) {
+    // Copy the audio samples into an output buffer.
+    output = new DataBuffer(decoded_audio_size);
+    output->SetDataSize(decoded_audio_size);
+    uint8* data = output->GetWritableData();
+    memcpy(data, decoded_audio_.get(), decoded_audio_size);
+  } else if (IsTimestampMarkerPacket(result, input)) {
+    // Nothing else to do here but update our estimation.
     estimated_next_timestamp_ = input->GetTimestamp() + input->GetDuration();
-    DecoderBase<AudioDecoder, Buffer>::OnDecodeComplete(statistics);
+  } else if (IsEndOfStream(result, decoded_audio_size, input)) {
+    // Create an end of stream output buffer.
+    output = new DataBuffer(0);
+    output->SetTimestamp(input->GetTimestamp());
+    output->SetDuration(input->GetDuration());
+  }
+
+  DecodeFinished(output, statistics);
+}
+
+void FFmpegAudioDecoder::DecodeFinished(
+    scoped_refptr<Buffer> output,
+    const PipelineStatistics& statistics) {
+  stats_callback_->Run(statistics);
+
+  if (output) {
+    DCHECK_GT(output_buffers_.size(), 0u);
+    output_buffers_.pop_front();
+
+    ConsumeAudioSamples(output);
+  }
+}
+
+void FFmpegAudioDecoder::ReadFromDemuxerStream() {
+  DCHECK(!output_buffers_.empty())
+      << "Reads should only occur if there are output buffers.";
+
+  pending_reads_++;

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

Add stopped check to make sure we don't call the demuxer stream if we have
received a Stop().

+  demuxer_stream_->Read(
+      NewCallback(this, &FFmpegAudioDecoder::OnReadComplete));
+}
+
+void FFmpegAudioDecoder::OnReadComplete(Buffer* buffer) {
+  // TODO(scherkus): change DemuxerStream::Read() to use scoped_refptr<> for
+  // callback.
+  scoped_refptr<Buffer> ref_buffer(buffer);
+  message_loop_->PostTask(
+      FROM_HERE,
+      NewRunnableMethod(this, &FFmpegAudioDecoder::DoDecodeInputBuffer,

[acolwell GONE FROM CHROMIUM, 2011/05/13 19:35:37]

Put this in an message loop guard and copy DoDecodeInputBuffer code in here?

+                        ref_buffer));
+}
+
+void FFmpegAudioDecoder::UpdateDurationAndTimestamp(
+    Buffer* input,
+    DataBuffer* output) {
+  // Always calculate duration based on the actual number of samples decoded.
+  base::TimeDelta duration = CalculateDuration(output->GetDataSize());
+  output->SetDuration(duration);
+
+  // Use the incoming timestamp if it's valid.
+  if (input->GetTimestamp() != kNoTimestamp) {
+    output->SetTimestamp(input->GetTimestamp());
+    estimated_next_timestamp_ = input->GetTimestamp() + duration;
     return;
   }
 
-  // Three conditions to meet to declare end of stream for this decoder:
-  // 1. FFmpeg didn't read anything.
-  // 2. FFmpeg didn't output anything.
-  // 3. An end of stream buffer is received.
-  if (result == 0 && output_buffer_size == 0 && input->IsEndOfStream()) {
-    DataBuffer* result_buffer = new DataBuffer(0);
-    result_buffer->SetTimestamp(input->GetTimestamp());
-    result_buffer->SetDuration(input->GetDuration());
-    EnqueueResult(result_buffer);
+  // Otherwise use an estimated timestamp and attempt to update the estimation
+  // as long as it's valid.
+  output->SetTimestamp(estimated_next_timestamp_);
+  if (estimated_next_timestamp_ != kNoTimestamp) {
+    estimated_next_timestamp_ += duration;
   }
-  DecoderBase<AudioDecoder, Buffer>::OnDecodeComplete(statistics);
 }
 
-base::TimeDelta FFmpegAudioDecoder::CalculateDuration(size_t size) {
-  int64 denominator = codec_context_->channels *
-      av_get_bits_per_sample_fmt(codec_context_->sample_fmt) / 8 *
-      codec_context_->sample_rate;
+base::TimeDelta FFmpegAudioDecoder::CalculateDuration(int size) {
+  // XXX: Could we make this function part of AudioDecoderConfig? Something like
+  // "I want a duration for this config based on # of bytes"?
+  int64 denominator = config_.channels_per_sample *
+      config_.bits_per_channel / 8 * config_.sample_rate;
   double microseconds = size /
       (denominator / static_cast<double>(base::Time::kMicrosecondsPerSecond));
   return base::TimeDelta::FromMicroseconds(static_cast<int64>(microseconds));
 }
 
-}  // namespace
+}  // namespace media