[Bug 725835] v4l2sink: Use GstVideoCropMeta to set overlay window if available

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=725835
  GStreamer | gst-plugins-good | git

--- Comment #4 from Nicolas Dufresne <nicolas.dufresne at collabora.co.uk> 2014-03-07 18:36:15 UTC ---
(In reply to comment #3)
> Crop and scale part for output device is also unclear in my mind at this
> moment.
> The spec say cropping ioctls on an output device determine the area where
> images are inserted. So i don't think we can really crop in this case using
> cropping ioctls.

Well, if you place your video at a negative location and make the window larger
then display, what you get is a crop (assuming the HW can scale).

> It seems that we can determine if a device does scaling or not with cropcaps.
> However it is not really clear how, maybe we should check if cropcaps bounds
> are equal to cropcaps defrect.

I made the same conclusion here.

> For now, I will try first to ensure that pixel aspect ratio remains the same

I'd love to know, specially, how to userspace know that the driver is doing it
right.

> Moreover, since all this behavior with output device seems to be an abuse of
> the V4L2 cropping/overlay API, it could be interesting to rely on the
> experimental selection API. Drawback is device compatibilty issue.

Heard about this one, obviously not yet implemented in GStreamer, but I'd like
to know more at some point.

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