Change MediaStreamVideoSource to output different resolutions to different tracks depending on the …

content/renderer/media/video_track_adapter.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 CONTENT_RENDERER_MEDIA_VIDEO_TRACK_ADAPTER_H_
+#define CONTENT_RENDERER_MEDIA_VIDEO_TRACK_ADAPTER_H_
+
+#include <vector>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "content/renderer/media/media_stream_video_track.h"
+#include "media/base/video_frame.h"
+
+namespace content {
+
+// VideoTrackAdapter is a helper class used by MediaStreamVideoSource used for
+// adapting the video resolution from a source implementation to the resolution
+// a track requires. Different tracks can have different resolution constraints.
+// The constraints can be set as max width and height as well as max and min
+// aspect ratio.
+// Video frames are delivered to a track using a VideoCaptureDeliverFrameCB on
+// the IO-thread.
+// Adaptations is done by wrapping the original media::VideoFrame in a new
+// media::VideoFrame with a new visible_rect and natural_size.
+class VideoTrackAdapter

[mcasas, 2014/05/07 14:10:43]

I seem to understand from VideoTrackAdapter structure that it can perform
different adaptations, but these class-docos only talk about
resolution/aspect-ratio/visible-region adjustments. 

IOW if VTA is generic, then mention the current use case as a particular
adaptation, otherwise surface VFRA and skip VTA altogether.

[perkj_chrome, 2014/05/08 11:29:47]

Not sure what you mean. It can only change the resolution.

+    : public base::RefCountedThreadSafe<VideoTrackAdapter> {
+ public:
+  explicit VideoTrackAdapter(
+      const scoped_refptr<base::MessageLoopProxy>& io_message_loop);
+
+  // Register |track| to receive video frames in |frame_callback| with
+  // a resolution within the boundaries of the arguments.
+  // Must be called on the main render thread.
+  void AddTrack(MediaStreamVideoTrack* track,
+                VideoCaptureDeliverFrameCB frame_callback,
+                int max_width, int max_height,
+                double min_aspect_ratio,
+                double max_aspect_ratio);
+  void RemoveTrack(MediaStreamVideoTrack* track);
+
+  // Delivers |frame| to all tracks that have registered a callback.
+  // Must be called on the IO-thread.
+  void DeliverFrameOnIO(
+      const scoped_refptr<media::VideoFrame>& frame,
+      const media::VideoCaptureFormat& format);
+
+  const scoped_refptr<base::MessageLoopProxy>& io_message_loop() {
+    return io_message_loop_;
+  }
+
+ private:
+  virtual ~VideoTrackAdapter();
+  friend class base::RefCountedThreadSafe<VideoTrackAdapter>;
+
+  void AddTrackOnIO(MediaStreamVideoTrack* track,
+                    VideoCaptureDeliverFrameCB frame_callback,
+                    int max_width, int max_height,
+                    double min_aspect_ratio,
+                    double max_aspect_ratio);
+  void RemoveTrackOnIO(MediaStreamVideoTrack* track);
+
+  base::ThreadChecker thread_checker_;
+  scoped_refptr<base::MessageLoopProxy> io_message_loop_;
+
+  // VideoFrameResolutionAdapter is an inner class that is created on the main
+  // render thread but operates on the IO-thread. It does the resolution
+  // adaptation and delivers frames to all registered tracks on the IO-thread.
+  class VideoFrameResolutionAdapter;
+  typedef std::vector<scoped_refptr<VideoFrameResolutionAdapter> >

[mcasas, 2014/05/07 14:10:43]

std::list? Seems that you only used it for push_back() and iterator search
anyway.

[perkj_chrome, 2014/05/08 11:29:47]

vector seems to be prefered in Chrome. Its far more widely used than lists.
Performance vice I don't think it matters since there will only be one or very
few items in this list.

+      FrameAdapters;
+  FrameAdapters adapters_;
+
+  DISALLOW_COPY_AND_ASSIGN(VideoTrackAdapter);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_VIDEO_TRACK_ADAPTER_H_