video: Add a linear/affine transformation matrix meta
Submitted by Sebastian Dröge @slomo
Link to original bug (#738914)
Description
+++ 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.