Mac platform was not treating 8bit PCM audio as unsigned data.

If bits per channel is 8, open the stream as unsigned and use 128 as the silence value.

BUG=70730
TEST=media_unittests and manual testing of a bunch of audio files (8 bit and others).

Review URL: http://codereview.chromium.org/6689003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@80181 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 15 insertions, 4 deletions

diff --git a/media/audio/mac/audio_output_mac.cc b/media/audio/mac/audio_output_mac.cc
index ab96bd6..c940b5a 100644
--- a/media/audio/mac/audio_output_mac.cc
+++ b/media/audio/mac/audio_output_mac.cc
@@ -56,8 +56,7 @@ PCMQueueOutAudioOutputStream::PCMQueueOutAudioOutputStream(
   // packet is always one frame.
   format_.mSampleRate = params.sample_rate;
   format_.mFormatID = kAudioFormatLinearPCM;
-  format_.mFormatFlags = kLinearPCMFormatFlagIsPacked |
-                         kLinearPCMFormatFlagIsSignedInteger;
+  format_.mFormatFlags = kLinearPCMFormatFlagIsPacked;
   format_.mBitsPerChannel = params.bits_per_sample;
   format_.mChannelsPerFrame = params.channels;
   format_.mFramesPerPacket = 1;
@@ -66,6 +65,10 @@ PCMQueueOutAudioOutputStream::PCMQueueOutAudioOutputStream(
 
   packet_size_ = params.GetPacketSize();
 
+  if (params.bits_per_sample > 8) {
+    format_.mFormatFlags |= kLinearPCMFormatFlagIsSignedInteger;
+  }
+
   // Silence buffer has a duration of 6ms to simulate the behavior of Windows.
   // This value is choosen by experiments and macs cannot keep up with
   // anything less than 6ms.
@@ -219,7 +222,15 @@ void PCMQueueOutAudioOutputStream::RenderCallback(void* p_this,
   if (!filled) {
     CHECK(audio_stream->silence_bytes_ <= static_cast<int>(capacity));
     filled = audio_stream->silence_bytes_;
-    memset(buffer->mAudioData, 0, filled);
+
+    // Assume unsigned audio.
+    int silence_value = 128;
+    if (audio_stream->format_.mBitsPerChannel > 8) {
+      // When bits per channel is greater than 8, audio is signed.
+      silence_value = 0;
+    }
+
+    memset(buffer->mAudioData, silence_value, filled);
     static_cast<AudioQueueUserData*>(buffer->mUserData)->empty_buffer = true;
   } else if (filled > capacity) {
     // User probably overran our buffer.
@@ -242,7 +253,7 @@ void PCMQueueOutAudioOutputStream::RenderCallback(void* p_this,
 
   buffer->mAudioDataByteSize = filled;
 
-  // Incremnet bytes by amount filled into audio buffer if this is not a
+  // Increment bytes by amount filled into audio buffer if this is not a
   // silence buffer.
   if (!static_cast<AudioQueueUserData*>(buffer->mUserData)->empty_buffer)
     audio_stream->pending_bytes_ += filled;