[Bug 738914] New: video: Add a linear/affine transformation matrix meta

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=738914
  GStreamer | gst-plugins-base | git

           Summary: video: Add a linear/affine transformation matrix meta
    Classification: Platform
           Product: GStreamer
           Version: git
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: Normal
         Component: gst-plugins-base
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: slomo at coaxion.net
         QAContact: gstreamer-bugs at lists.freedesktop.org
                CC: bugzilla at hadess.net, msameer at foolab.org,
                    t.i.m at zen.co.uk, slomo at coaxion.net,
                    jstultz at hotmail.com, michael at doube.net,
                    phil at base-art.net, james.hodapp at gmail.com,
                    thiagossantos at gmail.com, ylatuya at gmail.com,
                    nicolas.dufresne at collabora.co.uk
        Depends on: 679522
     GNOME version: ---


+++ This bug was initially created as a clone of Bug #679522 +++

In Quicktime/MP4 we can get an arbitrary transformation matrix that should be
applied to the video before displaying. In other contexts we also get that, or
sometimes just a rotation angle which could be expressed like this too.

There should probably be a meta that contains such an arbitrary 3x3
transformation matrix, can be negotiated inside the pipeline and implemented by
sinks or other elements.

Additionally there might be constraints on what elements are implementing, e.g.
some might only implement n*90° rotations and flips (videoflip element), which
might be something that should be possible to negotiate.

Also an open question is what should happen with transformations that produce a
non-rectangle output (e.g. rotations or shears). I would say they should create
a bigger frame with black borders, but what also would be valid is cropping
everything that goes over the frame size.

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