Fix Linux audio playback for short files

media/audio/linux/alsa_output.cc

Index: media/audio/linux/alsa_output.cc
diff --git a/media/audio/linux/alsa_output.cc b/media/audio/linux/alsa_output.cc
index d8e502cf7699b60b49c794be0faa2c289f8b0408..3b5cc4d1bdfc51ab534edb702b8637b25304d7b7 100644
--- a/media/audio/linux/alsa_output.cc
+++ b/media/audio/linux/alsa_output.cc
@@ -395,6 +395,14 @@ void AlsaPcmOutputStream::StartTask() {
     return;
   }
 
+  if (shared_data_.state() != kIsPlaying) {
+    return;
+  }
+
+  // Before starting, the buffer might have audio from previous user of this
+  // device.
+  buffer_->Clear();

[scherkus (not reviewing), 2011/04/11 18:22:39]

final question: are we sure this won't clobber any previous sound?

[davejcool, 2011/04/13 01:24:05]

If there is something in buffer_, it must be from the previous usage of this
stream, and is invalid.  Only after starting is the first ScheduleNextWrite()
called, so the buffer_ can't have anything we need in it yet for the stream
currently starting, but it could have something leftover from the previous usage
of this stream.

At this time we expect the buffer to be zero length, if it's not, it will throw
off our computation of the hardware_delay in BufferPacket().  

+
   // When starting again, drop all packets in the device and prepare it again
   // incase we are restarting from a pause state and need to flush old data.
   int error = wrapper_->PcmDrop(playback_handle_);
@@ -538,6 +546,10 @@ void AlsaPcmOutputStream::WritePacket() {
     return;
   }
 
+  if (shared_data_.state() == kIsStopped) {
+    return;
+  }
+
   CHECK_EQ(buffer_->forward_bytes() % bytes_per_output_frame_, 0u);
 
   const uint8* buffer_data;
@@ -579,6 +591,13 @@ void AlsaPcmOutputStream::WritePacket() {
       // Seek forward in the buffer after we've written some data to ALSA.
       buffer_->Seek(frames_written * bytes_per_output_frame_);
     }
+  } else {
+    // If nothing left to write and playback hasn't started yet, start it now.
+    // This ensures that shorter sounds will still play.
+    if ((wrapper_->PcmState(playback_handle_) == SND_PCM_STATE_PREPARED) &&
+        GetCurrentDelay() > 0) {
+      wrapper_->PcmStart(playback_handle_);
+    }
   }
 }
 
@@ -589,6 +608,10 @@ void AlsaPcmOutputStream::WriteTask() {
     return;
   }
 
+  if (shared_data_.state() == kIsStopped) {
+    return;
+  }
+
   bool source_exhausted;
   BufferPacket(&source_exhausted);
   WritePacket();