Tab Capture: Backing store readbacks to YV12 VideoFrames.

media/video/capture/video_capture_device.h

Index: media/video/capture/video_capture_device.h
diff --git a/media/video/capture/video_capture_device.h b/media/video/capture/video_capture_device.h
index fdfd8bea25b94fed9848241e5745323f8bdffd4a..d66c652397db96c875f2a5a3dcc73a59fd9eee38 100644
--- a/media/video/capture/video_capture_device.h
+++ b/media/video/capture/video_capture_device.h
@@ -36,15 +36,23 @@ class MEDIA_EXPORT VideoCaptureDevice {
 
   class MEDIA_EXPORT EventHandler {
    public:
-    // Captured a new video frame.
+    // Captured a new video frame as a raw buffer. The size, color format, and
+    // layout are taken from the parameters specified by an earlier call to
+    // OnFrameInfo. |data| must be packed, with no padding between rows and/or

[scherkus (not reviewing), 2013/02/05 22:40:44]

pedantic nit: similar to using || around variable references in comments we like
to annotate function call references with () at the end to help distinguish
TypeNames from FunctionCalls().

[ncarter (slow), 2013/02/06 23:54:44]

Done.

+    // color planes.
     virtual void OnIncomingCapturedFrame(const uint8* data,
                                          int length,
                                          base::Time timestamp) = 0;
+    // Captured a new video frame, held in a VideoFrame container. |frame| must
+    // be allocated as RGB32, YV12 or I420, and the size must match that
+    // specified by an earlier call to OnFrameInfo.

[scherkus (not reviewing), 2013/02/05 22:40:44]

s/OnFrameInfo/OnFrameInfo()/

[ncarter (slow), 2013/02/06 23:54:44]

Done.

+    virtual void OnIncomingCapturedVideoFrame(media::VideoFrame* frame,

[scherkus (not reviewing), 2013/02/05 22:40:44]

I'm firmly in the camp that likes uses const scoped_refptr<T>& when passing
around ref-counted types (pros: self-documenting, callees won't forget to ref it
if they need to, no need for make_scoped_refptr(), cons: cumbersome)

[ncarter (slow), 2013/02/06 23:54:44]

Changing T*'s to const scoped_refptr<T>&'s would be a whole bunch of text
editing, and I happen to know that all affected lines are likely to churn in the
very near future -- because of the possibility of allocating a VideoFrame backed
by the DIB, I think we should move to a model where VideoFrames are allocated by
the caller of CopyFromBackingStoreToVideoFrame, and the callback gets a 'bool
success' param (Ironically, this is the model we just moved away from, for
CopyFromBackingStore/PlatformBitmap).

So, my inclination is to simply move to the new caller-allocated model
immediately, in this CL. I'm prepping it now.

[scherkus (not reviewing), 2013/02/07 18:25:03]

SGTM

+                                              base::Time timestamp) = 0;

[scherkus (not reviewing), 2013/02/05 22:40:44]

FYI VideoFrame has a Get/SetTimestamp() field, although it uses TimeDeltas :|

[ncarter (slow), 2013/02/06 23:54:44]

Yeah, I'm aware of that and I think it would be nice to unify it, but certainly
not in this change (I gather it would mean plumbing an origin timestamp to a
number of places).

[scherkus (not reviewing), 2013/02/07 18:25:03]

Agreed -- I believe VF (and other media buffer-ish classes) should be using
base::Time but that's way beyond the scope of this CL.

     // An error has occurred that can not be handled
     // and VideoCaptureDevice must be DeAllocated.
     virtual void OnError() = 0;
     // Called when VideoCaptureDevice::Allocate has been called
-    // to inform of the resulting frame size and color format.
+    // to inform of the resulting frame size.
     virtual void OnFrameInfo(const VideoCaptureCapability& info) = 0;
 
    protected: