Provide unplayed bytes ALSA implementation of audio

BUG=19921
TEST=play an video track on linux, AV should be in sync.

Use snd_pcm_delay() to provide the number of unplayed bytes in linux's
audio implementation. This information will correct the sync problem
for linux.

Review URL: http://codereview.chromium.org/173288

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@24163 0039d316-1c4b-4281-b951-d872f2087c98

4 files changed, 32 insertions, 3 deletions

diff --git a/media/audio/linux/alsa_output.cc b/media/audio/linux/alsa_output.cc
index 8a59e33..96a2e4b 100644
--- a/media/audio/linux/alsa_output.cc
+++ b/media/audio/linux/alsa_output.cc
@@ -389,10 +389,28 @@ void AlsaPcmOutputStream::BufferPacket(Packet* packet) {
 
   // Request more data if we don't have any cached.
   if (packet->used >= packet->size) {
+    // Before making a request to source for data. We need to determine the
+    // delay (in bytes) for the requested data to be played.
+    snd_pcm_sframes_t delay;
+    int error = wrapper_->PcmDelay(playback_handle_, &delay);
+    if (error < 0) {
+      error = wrapper_->PcmRecover(playback_handle_,
+                                   error,
+                                   kPcmRecoverIsSilent);
+      if (error < 0) {
+        LOG(ERROR) << "Failed querying delay: " << wrapper_->StrError(error);
+      }
+
+      // TODO(hclam): If we cannot query the delay, we may want to stop
+      // the playback and report an error.
+      delay = 0;
+    } else {
+      delay *= bytes_per_frame_;
+    }
+
     packet->used = 0;
-    // TODO(hclam): Provide pending bytes.
     packet->size = shared_data_.OnMoreData(this, packet->buffer.get(),
-                                           packet->capacity, 0);
+                                           packet->capacity, delay);
     CHECK(packet->size <= packet->capacity) << "Data source overran buffer.";
 
     // This should not happen, but incase it does, drop any trailing bytes
diff --git a/media/audio/linux/alsa_output_unittest.cc b/media/audio/linux/alsa_output_unittest.cc
index d736d93..d13da89 100644
--- a/media/audio/linux/alsa_output_unittest.cc
+++ b/media/audio/linux/alsa_output_unittest.cc
@@ -24,6 +24,7 @@ class MockAlsaWrapper : public AlsaWrapper {
   MOCK_METHOD1(PcmClose, int(snd_pcm_t* handle));
   MOCK_METHOD1(PcmPrepare, int(snd_pcm_t* handle));
   MOCK_METHOD1(PcmDrop, int(snd_pcm_t* handle));
+  MOCK_METHOD2(PcmDelay, int(snd_pcm_t* handle, snd_pcm_sframes_t* delay));
   MOCK_METHOD3(PcmWritei, snd_pcm_sframes_t(snd_pcm_t* handle,
                                             const void* buffer,
                                             snd_pcm_uframes_t size));
@@ -272,6 +273,9 @@ TEST_F(AlsaPcmOutputStreamTest, StartStop) {
 
   // Expect the pre-roll.
   MockAudioSourceCallback mock_callback;
+  EXPECT_CALL(mock_alsa_wrapper_, PcmDelay(kFakeHandle, _))
+      .Times(2)
+      .WillRepeatedly(DoAll(SetArgumentPointee<1>(0), Return(0)));
   EXPECT_CALL(mock_callback,
               OnMoreData(test_stream_.get(), _, kTestPacketSize, 0))
       .Times(2)
@@ -361,9 +365,11 @@ TEST_F(AlsaPcmOutputStreamTest, BufferPacket) {
 
   // Return a partially filled packet.
   MockAudioSourceCallback mock_callback;
+  EXPECT_CALL(mock_alsa_wrapper_, PcmDelay(_, _))
+      .WillOnce(DoAll(SetArgumentPointee<1>(1), Return(0)));
   EXPECT_CALL(mock_callback,
               OnMoreData(test_stream_.get(), packet_.buffer.get(),
-                         packet_.capacity, 0))
+                         packet_.capacity, kTestBytesPerFrame))
       .WillOnce(Return(10));
 
   test_stream_->shared_data_.set_source_callback(&mock_callback);
diff --git a/media/audio/linux/alsa_wrapper.cc b/media/audio/linux/alsa_wrapper.cc
index 9557cac..8463686 100644
--- a/media/audio/linux/alsa_wrapper.cc
+++ b/media/audio/linux/alsa_wrapper.cc
@@ -29,6 +29,10 @@ int AlsaWrapper::PcmDrop(snd_pcm_t* handle) {
   return snd_pcm_drop(handle);
 }
 
+int AlsaWrapper::PcmDelay(snd_pcm_t* handle, snd_pcm_sframes_t* delay) {
+  return snd_pcm_delay(handle, delay);
+}
+
 snd_pcm_sframes_t AlsaWrapper::PcmWritei(snd_pcm_t* handle,
                                          const void* buffer,
                                          snd_pcm_uframes_t size) {
diff --git a/media/audio/linux/alsa_wrapper.h b/media/audio/linux/alsa_wrapper.h
index a3dafbb..d7686dd 100644
--- a/media/audio/linux/alsa_wrapper.h
+++ b/media/audio/linux/alsa_wrapper.h
@@ -20,6 +20,7 @@ class AlsaWrapper {
   virtual int PcmClose(snd_pcm_t* handle);
   virtual int PcmPrepare(snd_pcm_t* handle);
   virtual int PcmDrop(snd_pcm_t* handle);
+  virtual int PcmDelay(snd_pcm_t* handle, snd_pcm_sframes_t* delay);
   virtual snd_pcm_sframes_t PcmWritei(snd_pcm_t* handle,
                                       const void* buffer,
                                       snd_pcm_uframes_t size);