When CEA-608 is embedded in MP4 each packet consists of
cc_data_1 and cc_data_2 only. The marker_bits, cc_valid
and cc_type are implicit. As a result playback of CEA-608
embedded in MP4 broke when we started passing the extra
byte for the TS case (and adjusted the decoder to assume
the byte was present).
This change introduces a special mimeType for the case
where the byte is implicit (!). An alternative option
was to insert the extra byte every 2 bytes in the MP4
extractor, but this is really quite fiddly to get right.
Also made the loops in the 608/708 decoders robust against
input of the wrong length.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=140609304
