Exposes a shlib interface for media/audio path.

chromecast/public/cast_audio_output_device.h

+// Copyright 2015 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.
+
+#ifndef CHROMECAST_PUBLIC_CAST_AUDIO_OUTPUT_DEVICE_H_
+#define CHROMECAST_PUBLIC_CAST_AUDIO_OUTPUT_DEVICE_H_
+
+#include "cast_audio_output_stream.h"
+#include "chromecast_export.h"
+
+namespace chromecast {
+
+class TaskRunner;
+
+namespace media {

[halliwell, 2015/07/29 15:06:57]

we've been putting the other chromecast::media interfaces in
chromecast/public/media directory.  VIdeoPlane is an exception, it was the first
class added ... we should probably move it.  But let's move these as they're
new.

[slan, 2015/07/29 19:51:55]

Done.

+
+// This is an interface used to provide platform-specific audio streams.
+// Implementations of this interface should survive for the duration of the
+// process.
+
+// Note: This interface should be implemented by third parties seeking to
+// provide an audio manager platform for Cast. CastAudioManager will call
+// this interface.
+
+class CHROMECAST_EXPORT CastAudioOutputDevice {
+ public:
+  virtual ~CastAudioOutputDevice() {}
+
+  // Returns the maximum number of output streams allowed.
+  virtual int GetMaximumOutputStreamsAllowed() const = 0;
+
+  // Returns the preferred output stream parameters. The caller may inject
+  // |suggested| parameters, but it is left to the implementation to decide
+  // which of these to return.
+  virtual AudioParameters GetPreferredOutputStreamParameters(
+      const AudioParameters& suggested) const = 0;
+
+  // Creates the output stream with parameters described by |params|. Caller
+  // does not take ownership of the returned stream. All callbacks to
+  // CastAudioOutputStream::AudioSourceCallback objects should be made on the
+  // same thread on which this message is called. |task_runner| may be used as
+  // as a media rendering thread and should be non-null.

[halliwell, 2015/07/29 15:06:57]

The task_runner part seems very vague/unclear to me.  As background, in the CMA
case, I added it because:
* We have a clear threading model where we make all calls into vendor code on a
specific, designated "media thread"
* In order to simplify thread safety in implementations, it's highly desirable
for vendors to have the ability to schedule other work on that same thread. 
Hence the task runner.

This comment seems less clear to me.  What thread(s) are we calling the APIs in
this interface on, to start with?

I should probably go find the internal review as well.

[slan, 2015/07/29 19:51:55]

Clarified, based on our offline conversation.

+  virtual CastAudioOutputStream* MakeOutputStream(
+      const AudioParameters& params,
+      chromecast::TaskRunner* task_runner) = 0;

[gunsch, 2015/07/29 17:22:36]

chromecast:: not necessary

[slan, 2015/07/29 19:51:55]

Done.

+};
+
+}  // namespace media
+}  // namespace chromecast
+
+#endif  // CHROMECAST_PUBLIC_CAST_AUDIO_OUTPUT_DEVICE_H_