Allow media track switching.

media/renderers/audio_renderer_impl.cc

Index: media/renderers/audio_renderer_impl.cc
diff --git a/media/renderers/audio_renderer_impl.cc b/media/renderers/audio_renderer_impl.cc
index 7cb22ffb1695abb831acbfac99a6b19983c33dae..955c60f87c595969ae5c2bc6fabf82f5c17b99e1 100644
--- a/media/renderers/audio_renderer_impl.cc
+++ b/media/renderers/audio_renderer_impl.cc
@@ -36,13 +36,11 @@ namespace media {
 AudioRendererImpl::AudioRendererImpl(
     const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
     media::AudioRendererSink* sink,
-    ScopedVector<AudioDecoder> decoders,
+    const CreateAudioDecodersCB& create_audio_decoders_cb,
     const scoped_refptr<MediaLog>& media_log)
     : task_runner_(task_runner),
       expecting_config_changes_(false),
       sink_(sink),
-      audio_buffer_stream_(
-          new AudioBufferStream(task_runner, std::move(decoders), media_log)),
       media_log_(media_log),
       client_(nullptr),
       tick_clock_(new base::DefaultTickClock()),
@@ -51,6 +49,7 @@ AudioRendererImpl::AudioRendererImpl(
       last_decoded_channel_layout_(CHANNEL_LAYOUT_NONE),
       playback_rate_(0.0),
       state_(kUninitialized),
+      create_audio_decoders_cb_(create_audio_decoders_cb),
       buffering_state_(BUFFERING_HAVE_NOTHING),
       rendering_(false),
       sink_playing_(false),
@@ -59,9 +58,7 @@ AudioRendererImpl::AudioRendererImpl(
       rendered_end_of_stream_(false),
       is_suspending_(false),
       weak_factory_(this) {
-  audio_buffer_stream_->set_config_change_observer(base::Bind(
-      &AudioRendererImpl::OnConfigChange, weak_factory_.GetWeakPtr()));
-
+  DCHECK(!create_audio_decoders_cb_.is_null());

[xhwang, 2017/03/27 19:13:53]

FYI: 

I think you can do this now:

DCHECK(create_audio_decoders_cb_);

https://cs.chromium.org/chromium/src/base/callback_internal.h?rcl=5f5b9df5535...

But feel free to ignore for consistency with existing code

[servolk, 2017/03/27 22:34:12]

Nice, thanks, I didn't know about this. Done.

   // Tests may not have a power monitor.
   base::PowerMonitor* monitor = base::PowerMonitor::Get();
   if (!monitor)
@@ -334,12 +331,23 @@ void AudioRendererImpl::Initialize(DemuxerStream* stream,
   DCHECK(stream);
   DCHECK_EQ(stream->type(), DemuxerStream::AUDIO);
   DCHECK(!init_cb.is_null());
-  DCHECK_EQ(kUninitialized, state_);
+  DCHECK(state_ == kUninitialized || state_ == kFlushed);
   DCHECK(sink_.get());
 
+  // If we are re-initializing playback (e.g. switching media tracks), stop the
+  // sink first.
+  if (state_ == kFlushed)
+    sink_->Stop();
+
   state_ = kInitializing;
   client_ = client;
 
+  audio_buffer_stream_ = base::MakeUnique<AudioBufferStream>(
+      task_runner_, create_audio_decoders_cb_.Run(), media_log_);
+
+  audio_buffer_stream_->set_config_change_observer(base::Bind(
+      &AudioRendererImpl::OnConfigChange, weak_factory_.GetWeakPtr()));
+
   // Always post |init_cb_| because |this| could be destroyed if initialization
   // failed.
   init_cb_ = BindToCurrentLoop(init_cb);