[Bug 777475] compositor : Issue in computing position when pixel-aspect-ratio is not 1/1

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=777475

Matthew Waters (ystreet00) <ystreet00 at gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |ystreet00 at gmail.com

--- Comment #1 from Matthew Waters (ystreet00) <ystreet00 at gmail.com> ---
pixel-aspect-ratio=2/1 by definition is a stretched video and the lack of a
pixel-aspect-ratio on the output caps (resulting in a default of 1/1), the
second pipeline is behaving as expected, i.e. 100x100 at a PAR of 2/1 is
transformed into 200x100 at a PAR of 1/1.  It's the exact same
pipeline/functionality as:
videotestsrc ! video/x-raw,pixel-aspect-ratio=2/1 ! videoscale ! autovideosink

As for positioning in the first pipeline, the positioning happens in relation
to the output position of which the input has been scaled according to the
width/height/PAR into the output width/height/PAR.

In the first pipeline example, this manifests in the following way.
1. output PAR is 1/1
2. the output size for the first stream is calculated from the width/height and
PAR to be 200x100 in the output canvas which is placed at 0,0.
3. the output size for the second stream is calculated from the width/height
and PAR to be 200x100 in the output canvas which is placed at 100,0.

Thus output size of 300x100 and the streams overlapping.

This is calculated here:
https://cgit.freedesktop.org/gstreamer/gst-plugins-bad/tree/gst/compositor/compositor.c#n217
and the same process is undertaken by any video sink that deals with non 1/1
PAR.

As such, I don't think there is a bug here.

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