Use of the GAP flag is not really correct here and makes it difficult to
handle real GAP buffers in deinterlace. The RFF flag is unused and can
be reused with similar semantics - the buffers marked with RFF that are
in a telecine state contain only unneeded repeated fields and so can be
dropped.
This element analyses video buffers to identify if they are progressive,
interlaced or telecined and outputs buffers with appropriate flags for a
downstream element (which will be the deinterlace element, after some
forthcoming modifications) to be able to output progressive frames and
adjust timestamps resulting in a progressive stream.
