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| and |flush_cb| with Closures.

[tim (not reviewing), 2014/08/22 22:26:42]

nit: Looks like you already did this for |flush_cb|

[xhwang, 2014/08/22 22:48:23]

Done.

+  //
+  // 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 |flush_cb| when completed.
+  virtual void Flush(const base::Closure& flush_cb) = 0;
+
+  // Starts rendering from |time|.
+  // TODO(xhwang): Switch to SetMediaTime() + StartPlaying() model?

[scherkus (not reviewing), 2014/08/22 20:50:01]

does this still need to be done? should we chat about this?

[xhwang, 2014/08/22 22:48:23]

Dropped the TODO. SetMediaTime() doesn't make too much sense here since
TimeSource is hidden.

+  virtual void StartPlayingFrom(base::TimeDelta time) = 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;
+
+  // Returns the current media time.
+  virtual base::TimeDelta GetMediaTime() = 0;

[scherkus (not reviewing), 2014/08/22 20:50:01]

note that this is the only method that gets called from multiple threads (I
believe)

[xhwang, 2014/08/22 22:48:23]

I have that comment in renderer_impl.h. I am hesitating to add it here since
this is an interface. In the original plan we could also have a browser side
Renderer impl, where this comment does apply.

+
+  // Returns whether |this| renders audio.
+  virtual bool HasAudio() = 0;
+
+  // Returns whether |this| renders video.
+  virtual bool HasVideo() = 0;
+
+  // Associates the |cdm| with this Renderer.
+  virtual void SetCdm(MediaKeys* cdm) = 0;

[scherkus (not reviewing), 2014/08/22 20:50:01]

does this need to be on the interface, or can it be on the impl?

[xhwang, 2014/08/22 22:48:23]

It needs to be on the interface because all Renderers could be associated with a
CDM. In the future, WebMediaPlayer::SetCDM() will be plumbed to this call.

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