media: Introduce Renderer interface and RendererImpl.

media/base/renderer.h

+// Copyright 2014 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 MEDIA_BASE_RENDERER_H_
+#define MEDIA_BASE_RENDERER_H_
+
+#include "base/callback.h"
+#include "base/time/time.h"
+#include "media/base/buffering_state.h"
+#include "media/base/media_export.h"
+#include "media/base/pipeline_status.h"
+
+namespace media {
+
+class MediaKeys;
+class TimeDeltaInterpolator;
+
+class MEDIA_EXPORT Renderer {
+ public:
+  typedef base::Callback<base::TimeDelta()> TimeDeltaCB;
+
+  Renderer();
+
+  // Stops rendering and fires any pending callbacks.
+  virtual ~Renderer();
+
+  // Initializes the Renderer, executing |init_cb| upon completion.
+  // TODO(xhwang): Provide a set of DemuxerStreams in Initialize().
+  // TODO(xhwang): Replace |init_cb|, |flush_cb| and |stop_cb| with Closures.

[damienv1, 2014/08/22 16:39:48]

1) I don't see a Stop. Is it missing ? (or Stop can only be done by destroying
the Renderer ?).

2) Regarding |init_cb|, |flush_cb|, I still don't know whether they should be
closure or not. But since this is not the scope of this CL, that can be
evaluated later on.

[xhwang, 2014/08/22 19:11:31]

Stop() has been folded into the dtor. Fixed the comment. Thanks for catching
this.
 
Yep. Let's iterate on this later.

+  //
+  // Permanent callbacks:
+  // - |statistics_cb|: Executed periodically with rendering statistics.
+  // - |time_cb|: Executed whenever time has advanced through rendering.
+  // - |ended_cb|: Executed when rendering has reached the end of stream.
+  // - |error_cb|: Executed if any error was encountered during rendering.
+  virtual void Initialize(const PipelineStatusCB& init_cb,
+                          const StatisticsCB& statistics_cb,
+                          const base::Closure& ended_cb,
+                          const PipelineStatusCB& error_cb,
+                          const BufferingStateCB& buffering_state_cb,
+                          const TimeDeltaCB& get_duration_cb) = 0;
+
+  // The following functions must be called after Initialize().
+
+  // Discards any buffered data, executing |done_cb| when completed.

[damienv1, 2014/08/22 16:39:48]

nit: done_cb VS flush_cb

[xhwang, 2014/08/22 19:11:31]

Done.

+  virtual void Flush(const base::Closure& flush_cb) = 0;
+
+  // Starts rendering from |timestamp|.
+  // TODO(xhwang): Switch to SetMediaTime() + StartPlaying() model?
+  virtual void StartPlayingFrom(base::TimeDelta timestamp) = 0;
+
+  // Updates the current playback rate. The default playback rate should be 1.
+  virtual void SetPlaybackRate(float playback_rate) = 0;
+
+  // Sets the output volume. The default volume should be 1.
+  virtual void SetVolume(float volume) = 0;
+
+  virtual base::TimeDelta GetMediaTime() = 0;
+
+  virtual bool HasAudio() = 0;
+
+  virtual bool HasVideo() = 0;
+
+  // Associates the |cdm| with this Renderer.
+  virtual void SetCdm(MediaKeys* cdm) = 0;
+
+  // Helper functions for testing purposes. Must be called before Initialize().
+  virtual void DisableUnderflowForTesting();
+  virtual void SetTimeDeltaInterpolatorForTesting(
+      TimeDeltaInterpolator* interpolator);

[damienv1, 2014/08/22 16:39:48]

I don't think this should belong to the base class (Is there any way to put that
only in implementation class ?)
When you do some tests, you actually test an implementation.

[xhwang, 2014/08/22 19:11:31]

scherkus@ had the same comment. Removed and only have it in the impl.

+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(Renderer);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_RENDERER_H_