[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

Nicolas Dufresne <nicolas.dufresne> changed:

           What    |Removed                     |Added
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 Attachment #271119|none                        |needs-work
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--- Comment #1 from Nicolas Dufresne <nicolas.dufresne at collabora.co.uk> 2014-03-06 17:20:53 UTC ---
Review of attachment 271119:
 --> (https://bugzilla.gnome.org/review?bug=725835&attachment=271119)

I think it's indeed a good idea to handle crop meta, specially that we
advertise doing so

gst_query_add_allocation_meta (query, GST_VIDEO_CROP_META_API_TYPE, NULL);

Though, I this solution is not complete, and does not correlate with V4L2
specification. Overlay in V4L2 is designed initially for sources (capture) that
renders directly on top of the frame buffer. It is now experimentally accepted
for sink (output) though the effect need to be correlated with the crop
information in order to preserve aspect ratio. The spec is still very vague on
how to probe this. But what is stated is that both overlay and crop settings
can crop or scale. The spec also seem to say that there exist a way to check if
it's being scaled and what factor, but it's still very unclear in my mind.

http://linuxtv.org/downloads/v4l-dvb-apis/osd.html
http://linuxtv.org/downloads/v4l-dvb-apis/crop.html

Also, if overlay is not supported, fallback to using crop would be nice, and
vis-versa. There exist a rather large overlap between the two API.

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