MediaStream: Adding VideoTrackRecorder class and unittests

content/renderer/media/video_track_recorder.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 CONTENT_RENDERER_MEDIA_VIDEO_TRACK_RECORDER_H_
+#define CONTENT_RENDERER_MEDIA_VIDEO_TRACK_RECORDER_H_
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/strings/string_piece.h"
+#include "base/threading/thread_checker.h"
+#include "content/public/renderer/media_stream_video_sink.h"
+#include "third_party/WebKit/public/platform/WebMediaStreamTrack.h"
+#include "ui/gfx/geometry/size.h"
+
+namespace content {
+
+// VideoTrackRecorder is a MediaStreamVideoSink that encodes the video frames
+// received from a Stream Video Track. The class is constructed and used on a
+// single thread, namely the main Render thread. It has an internal VpxEncoder
+// that uses a worker thread for encoding.
+class CONTENT_EXPORT VideoTrackRecorder
+    : NON_EXPORTED_BASE(public MediaStreamVideoSink) {
+ public:
+  using OnEncodedVideoCB = base::Callback<void(const base::StringPiece& data,
+                                               base::TimeDelta timestamp,
+                                               bool is_key_frame)>;
+  using OnFirstFrameCB =
+      base::Callback<OnEncodedVideoCB(const gfx::Size& frame_size,

[miu, 2015/08/13 19:32:26]

IMO, this is even more complex than before (i.e., a callback that returns
another callback).

Why do we need a separate OnFirstFrameCB?  I think the same argument I made for
getting rid of |track_number| applies to this situation as well: In other words,
VideoTrackRecorder should not need to do anything special for the first frame. 
That's an implementation detail for using WebmMuxer.

The code for the function bound to OnEncodedVideoCB can easily check whether
it's the first time the OnEncodedVideoCB is being run, and deal with that
special case.  (See my earlier example.)

WDYT?

+                                      double frame_rate)>;
+
+  VideoTrackRecorder(const blink::WebMediaStreamTrack& track,
+                     const OnFirstFrameCB& on_first_frame_cb);
+  ~VideoTrackRecorder() override;
+
+ private:
+  friend class VideoTrackRecorderTest;
+
+  // Used to ping |encoder_->StartFrameEncode()| for testing.
+  void StartFrameEncodeForTesting(const scoped_refptr<media::VideoFrame>& frame,
+                                  const base::TimeTicks& capture_time);
+
+  // Used to check that we are destroyed on the same thread we were created.
+  base::ThreadChecker main_render_thread_checker_;
+
+  // We need to hold on to the Blink track to remove ourselves on dtor.
+  const blink::WebMediaStreamTrack track_;
+
+  // Forward declaration and member of an inner class to encode using VPx.
+  class VpxEncoder;
+  const scoped_refptr<VpxEncoder> encoder_;
+
+  DISALLOW_COPY_AND_ASSIGN(VideoTrackRecorder);
+};
+
+}  // namespace content
+#endif  // CONTENT_RENDERER_MEDIA_VIDEO_TRACK_RECORDER_H_