Chromecast: Play audio streams not supported by CMA via default renderer

chromecast/media/base/media_renderer.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_MEDIA_BASE_MEDIA_RENDERER_H_
+#define CHROMECAST_MEDIA_BASE_MEDIA_RENDERER_H_
+
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "media/base/renderer.h"
+
+namespace media {
+class DemuxerStreamProvider;
+}
+
+namespace chromecast {
+namespace media {
+class CmaRenderer;
+
+// Chromecast's custom media renderer which is capable of selecting an
+// appropriate media renderer at runtime depending on the content.
+// We'll look at media types of media streams present in DemuxerStreamProvider
+// and will use either CMA-based renderer (for media types that are supported by
+// our hardware decoder - H264 and VP8 video, AAC and Vorbis audio) or the
+// default Chrome media renderer (this will allow us to support audio codecs
+// like FLAC and Opus, which are decoded in software).
+class MediaRenderer : public ::media::Renderer {

[gunsch, 2015/03/03 00:06:40]

Can we give this a better name than just the interface it's implementing?
perhaps "SwitchingMediaRenderer" or something.

[servolk, 2015/03/03 00:46:53]

Done.

+ public:
+  MediaRenderer(
+      scoped_ptr<::media::Renderer> default_renderer,
+      scoped_ptr<CmaRenderer> cma_renderer);

[gunsch, 2015/03/03 00:06:40]

This API's kind of interesting... is it possible we'll ever need more renderers?
If so, what about an API that took pairs of "::media::Renderer,
base::Callback<bool(void)> use_renderer_if_this_returns_true" ?

Alternately, this could be conceptually simplified by just taking two
::media::Renderer instances. There's no reason to tie the API to CmaRenderer
specifically. If you did that, it'd probably be okay to leave this file in
chromecast/media/base/, since it no longer depends on chromecast/media/cma/.

[servolk, 2015/03/03 00:46:53]

Yes, the only reason I used CmaRenderer here explicitly was to get some minimal
type-checking and make it impossible to give the parameters in the wrong order.
But since this unnecessary dependency on CmaRenderer creates some issues, we can
switch to generic media::Renderer.
I think we should look into refactoring the whole media renderer creation model
in WebMediaPlayer, but that would need to be done in a separate CL.

+  ~MediaRenderer() override;
+
+  // ::media::Renderer implementation:
+  void Initialize(
+      ::media::DemuxerStreamProvider* demuxer_stream_provider,
+      const base::Closure& init_cb,
+      const ::media::StatisticsCB& statistics_cb,
+      const ::media::BufferingStateCB& buffering_state_cb,
+      const ::media::Renderer::PaintCB& paint_cb,
+      const base::Closure& ended_cb,
+      const ::media::PipelineStatusCB& error_cb) override;
+  void SetCdm(::media::CdmContext* cdm_context,
+              const ::media::CdmAttachedCB& cdm_attached_cb) override;
+  void Flush(const base::Closure& flush_cb) override;
+  void StartPlayingFrom(base::TimeDelta time) override;
+  void SetPlaybackRate(float playback_rate) override;
+  void SetVolume(float volume) override;
+  base::TimeDelta GetMediaTime() override;
+  bool HasAudio() override;
+  bool HasVideo() override;
+
+ private:
+  // Returns the pointer to the actual renderer being used
+  ::media::Renderer* GetRenderer() const;
+
+  ::media::DemuxerStreamProvider* demuxer_stream_provider_;
+  scoped_ptr<::media::Renderer> default_renderer_;
+  scoped_ptr<CmaRenderer> cma_renderer_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaRenderer);
+};
+
+}  // namespace media
+}  // namespace chromecast
+
+#endif  // CHROMECAST_MEDIA_BASE_MEDIA_RENDERER_H_