As previously discussed, the CrystalHD hardware returns exceptionally
useless information about interlaced h.264 content - to the extent
that it's not possible to distinguish MBAFF and PAFF content until
it's too late.

This change introduces use of the h264_parser to help bridge the
gap; it can indicate if the input data is PAFF fields or not.

With this clarity, some of heuristics can be removed from the code,
making this less convoluted.

Finally, I found an MBAFF clip that acts like non h.264 content so
I had to make allowances for that.

Note that I still cannot distinguish between two forms of PAFF,
where the hardware either returns individual fields or a field-pair.
It's not clear that there's even a spec relevant difference between
the two forms, as opposed to hardware ideosyncracies.