We normally expect each frame to come in its own PES packet,
but it seems that this is not always the case. This change
uses the frame rate in the stream to increment the frame
timestamp in the case of multiple frames contained within
a single PES.
Note that since we don't expect 100s of frames in a single
PES, or anything close to that really, the rounding errors
that may accumulate due to use of a frame duration should be
fine.
Issue: #1112
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=111499052
