I found another MBAFF sample where the input:output pattern is
the same as mpeg2 and vc1 (fieldpair input, individual field output).
While I'm not sure how you can output individual fields from MBAFF,
if I apply the mpeg2/vc1 handling to this file, it plays correctly.

So, this changes the detection algorithm to handle the known cases.

Whitespace will be fixed in a separate change.
Signed-off-by: Philip Langdale <philipl@overt.org>