known issues:

  - negotiation is shite.  I don't want to know about any failed
    negotiations or failed prerolls.

  - teardown sometimes fails.

  - sharing a GL context among a bunch of elements that stomp all
    over it is potential fail.


intel driver:

  - rendering to texture ignores the color matrix.  This causes any
    YUV->RGB conversion to fail.

  - YUY2 and UYVY conversions in the driver use the wrong matrix.