This stream uses what mpeg2 calls a general slice structure - some
macroblocks are not included in any slice, and are thus not coded.

In mpeg2, the rule is that the action a decoder takes between the
coded slices is undefined (see 6.1.2.1). Also all defined mpeg2
profiles use the restricted slice structure - so in practice the
general slice structure is never used.

In mpeg1, the slices as defined in 2.4.1 are supposed to not overlap
or have gaps in-between, so the general slice structure is basically
illegal. This stream still uses it so the decoder's behaviour is (just
as in mpeg2) undefined.

UCB's mpeg_play program seems to fill these non-coded blocks in black,
but I think this is only by chance not by design. libmpeg2, like the
mpeg2 reference decoder, has a different behaviour, it will not touch
the pixels betweent he coded slices, so they will keep whatever value
they had when vo_get_frame passed the picture. For this stream this
results in some ugly green blocks, but this is actually acceptable as
the stream is bogus.