[Bug 728045] omxvideodec: support cropping information

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=728045
  GStreamer | gst-omx | git

Nicolas Dufresne <nicolas.dufresne> changed:

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--- Comment #3 from Nicolas Dufresne <nicolas.dufresne at collabora.co.uk> 2014-04-17 14:47:12 UTC ---
Review of attachment 274494:
 --> (https://bugzilla.gnome.org/review?bug=728045&attachment=274494)

I had a long discussion about cropping yesterday and I think we made a
conclusion that this is not right. Here's why:

decoder -> (buffer crop x=10,y=10) -> converter -> videosink

You'll endup 10 pixels garbage on the right and bottom borders. The reason is
that the converter will convert up to width * bpp (rather then up to stride),
reducing the amount of processing when there is large padding. So instead of
that, you need to adjust the offset of you image, so the data pointer you get
from frame_map() points to the right place. This can be achieved easily filling
the GstVideoAlignment structure, and calling gst_video_info_align() before
copying the offset and stride array to the GstVideoMeta. VideoMeta need to be
supported downstream obviously.

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