[gstreamer-bugs] [Bug 530737] New: [GstBaseTransform] does not preserve caps order in _getcaps function

[GStreamer (bugzilla.gnome.org)]

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  GStreamer | gstreamer (core) | Ver: HEAD CVS
           Summary: [GstBaseTransform] does not preserve caps order in
                    _getcaps function
           Product: GStreamer
           Version: HEAD CVS
          Platform: Other
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: major
          Priority: Normal
         Component: gstreamer (core)
        AssignedTo: gstreamer-bugs at lists.sourceforge.net
        ReportedBy: julien at moutte.net
         QAContact: gstreamer-bugs at lists.sourceforge.net
     GNOME version: Unspecified
   GNOME milestone: Unspecified


When being asked the caps for a pad basetransform will obtain the peer caps,
filter them against corresponding template, transform them, filter them again
with the corresponding template.

This last filtering operation is not preserving caps order in a reliable way.
So say you have peer caps supporting only YUY2, once filtered it's still YUY2,
transform gets YUY2 first plus everything we can transform to, when filtering
against template it's pure lottery YUY2 can stay first but can go also go last.

A potential way to fix this problem would be to introduce a caps intersection
function which preserves the order of the first caps and we could use that
function when filtering against templates so that template order is considered
unimportant.


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