Fix Linux audio playback for short files

media/audio/linux/alsa_output.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // THREAD SAFETY
 //
 // The AlsaPcmOutputStream object's internal state is accessed by two threads:
 //
 //   client thread - creates the object and calls the public APIs.
 //   message loop thread - executes all the internal tasks including querying
@@ skipping 377 matching lines @@
   }
 }
 
 void AlsaPcmOutputStream::StartTask() {
   DCHECK_EQ(message_loop_, MessageLoop::current());
 
   if (stop_stream_) {
     return;
   }
 
+  // Before starting, the buffer might have audio from previous user of this
+  // device.
+  buffer_->Clear();

[Sergey Ulanov, 2011/03/31 22:04:46]

Does this mean we cut the sound that was playing before?

[davejcool, 2011/04/09 03:10:43]

By this time, the previous stream's usage of this device has already been
stopped.  So if there's something left in the buffer, it's from the previous
stream being stopped with audio still in the buffer.  Without this clear, often
the start or end of a sound gets cut off.  

+
   // 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_);
   if (error < 0 && error != -EAGAIN) {
     LOG(ERROR) << "Failure clearing playback device ("
                << wrapper_->PcmName(playback_handle_) << "): "
                << wrapper_->StrError(error);
     stop_stream_ = true;
     return;
   }
@@ skipping 164 matching lines @@
     } else {
       if (frames_written > frames) {
         LOG(WARNING)
             << "snd_pcm_writei() has written more frame that we asked.";
         frames_written = frames;
       }
 
       // 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()) {

[scherkus (not reviewing), 2011/03/31 22:08:10]

GetCurrentDelay() > 0 ?

[davejcool, 2011/04/09 03:10:43]

Yes, >0 is better, thanks!

+      wrapper_->PcmStart(playback_handle_);
+    }
   }
 }
 
 void AlsaPcmOutputStream::WriteTask() {
   DCHECK_EQ(message_loop_, MessageLoop::current());
 
   if (stop_stream_) {
     return;
   }
 
@@ skipping 321 matching lines @@
 }
 
 // Changes the AudioSourceCallback to proxy calls to.  Pass in NULL to
 // release ownership of the currently registered callback.
 void AlsaPcmOutputStream::SharedData::set_source_callback(
     AudioSourceCallback* callback) {
   DCHECK_EQ(MessageLoop::current(), state_transition_loop_);
   base::AutoLock l(lock_);
   source_callback_ = callback;
 }