Add video frame recording capability to Chromoting hosts.

remoting/host/video_frame_recorder.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 REMOTING_HOST_VIDEO_FRAME_RECORDER_H_
 #define REMOTING_HOST_VIDEO_FRAME_RECORDER_H_
 
 #include <stdint.h>
 #include <list>
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/single_thread_task_runner.h"
 
 namespace webrtc {
 class DesktopFrame;
 }
 
 namespace remoting {
 
 class VideoEncoder;
 
 // Allows sequences of DesktopFrames passed to a VideoEncoder to be recorded.
 //
-// VideoFrameRecorder is design to support applications which use a dedicated
+// VideoFrameRecorder is designed to support applications which use a dedicated
 // thread for video encoding, but need to manage that process from a "main"
 // or "control" thread.
 //
 // On the control thread:
 // 1. Create the VideoFrameRecorder on the controlling thread.
 // 2. Specify the amount of memory that may be used for recording.
 // 3. Call WrapVideoEncoder(), passing the actual VideoEncoder that will be
 //    used to encode frames.
 // 4. Hand the returned wrapper VideoEncoder of to the video encoding thread,
 //    to call in place of the actual VideoEncoder.
 // 5. Start/stop frame recording as necessary.
 // 6. Use NextFrame() to read each recorded frame in sequence.
 //
 // The wrapper VideoEncoder is designed to be handed off to the video encoding
 // thread, and used and torn down there.
 //
 // The VideoFrameRecorder and VideoEncoder may be torn down in any order; frame
 // recording will stop as soon as either is destroyed.
 
 class VideoFrameRecorder {
  public:
   VideoFrameRecorder();
   virtual ~VideoFrameRecorder();
 
   // Wraps the supplied VideoEncoder, returning a replacement VideoEncoder that
   // will route frames to the recorder, as well as passing them for encoding.
-  // This may be called at most once on each VideoFrameRecorder instance.
+  // The caller must delete the previous recording VideoEncoder, or call
+  // DetachVideoEncoderWrapper() before calling WrapVideoEncoder() to create
+  // a new wrapper.

[Jamie, 2014/08/01 19:53:51]

This seems fragile. Why can't Wrap call Detach automatically? Or are you relying
on the DCHECK to catch bad callers?

[Wez, 2014/08/01 22:33:56]

If you create a second wrapper then it'll replace the existing one, which will
stop having its frames recorded. I think it's preferable that the caller
indicate via Detach...() that that behaviour is acceptable.

   scoped_ptr<VideoEncoder> WrapVideoEncoder(scoped_ptr<VideoEncoder> encoder);
 
+  // Detaches the existing VideoEncoder wrapper, stopping it from recording.
+  void DetachVideoEncoderWrapper();
+
   // Enables/disables frame recording. Frame recording is initially disabled.
   void SetEnableRecording(bool enable_recording);
 
   // Sets the maximum number of bytes of pixel data that may be recorded.
   // When this maximum is reached older frames will be discard to make space
   // for new ones.
   void SetMaxContentBytes(int64_t max_content_bytes);
 
   // Pops the next recorded frame in the sequence, and returns it.
   scoped_ptr<webrtc::DesktopFrame> NextFrame();
@@ skipping 25 matching lines @@
 
   scoped_refptr<base::SingleThreadTaskRunner> caller_task_runner_;
   base::WeakPtrFactory<VideoFrameRecorder> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoFrameRecorder);
 };
 
 }  // namespace remoting
 
 #endif  // REMOTING_HOST_VIDEO_FRAME_RECORDER_H_