Handle audio device changes on Windows.

media/audio/audio_output_controller.cc

 // Copyright (c) 2012 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.
 
 #include "media/audio/audio_output_controller.h"
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "base/message_loop.h"
 #include "base/synchronization/waitable_event.h"
@@ skipping 348 matching lines @@
     done->Signal();
 }
 
 void AudioOutputController::OnDeviceChange() {
   DCHECK(message_loop_->BelongsToCurrentThread());
   DVLOG(1) << "Received OnDeviceChange() notification.";
 
   // We should always have a stream by this point.
   CHECK(stream_);
 
+  // We only need to reconnect low latency streams.
+  // TODO(dalecurtis): Ideally AudioOutputController shouldn't have to make this
+  // decision, but for now it's the only object which holds the necessary pieces
+  // of information.  Eventually we'll get rid of the non-low latency audio
+  // implementations and this can be dropped at that time.

[scherkus (not reviewing), 2012/10/23 02:23:11]

...not as long as we're shipping on XP

perhaps a better way to think of this is that the AudioManager should know if
it's running on an OS where low latency is available or not (i.e., XP, Linux)
and could make the policy decision as to whether streams need to be recreated
there

[DaleCurtis, 2012/10/23 03:28:20]

I was considering WaveOut on XP ~= low latency.  That's not a bad idea though,
we can use the command line flags (disable audio renderer mixer / resampler) to
determine if >Vista+Mac need stream recreation or not. We'll end up recreating
some streams which may not need it, but it would be unexpected behavior to a
user.

OnDeviceChange() is kind of a strange name then as the caller is expected to
take a specific action if it is received.

[henrika (OOO until Aug 14), 2012/10/23 07:38:06]

Can you make a few tests on a Win7 machine where you fake that you are on XP
(IsWasapi... returns false) to verify that it works?

[DaleCurtis, 2012/10/23 20:09:08]

What are you looking to test? I was planning to have a full unit test for
AudioDeviceListenerWin which manually fired the callbacks on Windows.

[DaleCurtis, 2012/10/24 00:09:27]

I decided to do this check in the platform specific audio manager, if the device
changes on a platform which supports low latency it will fire the request.  This
means non-low-latency streams will be recreated, but I don't think it'll be
unusual from the user's point of view since they just changed audio devices.

+  if (params_.format() != AudioParameters::AUDIO_PCM_LOW_LATENCY)
+    return;
+
   // Preserve the original state and shutdown the stream.
   State original_state = state_;
   stream_->Stop();
   stream_->Close();
   stream_ = NULL;
 
   // Recreate the stream, exit if we ran into an error.
   state_ = kRecreating;
   DoCreate();
   if (!stream_ || state_ == kError)
     return;
 
   // Get us back to the original state or an equivalent state.
   switch (original_state) {
     case kStarting:
     case kPlaying:
       DoPlay();
       return;
     case kCreated:
     case kPausedWhenStarting:
     case kPaused:
       // From the outside these three states are equivalent.
       return;
     default:
       NOTREACHED() << "Invalid original state.";
   }
 }
 
 }  // namespace media