In MatroskaExtractor TrueHD audio samples are joined into larger chunks. For
some streams the resulting chunked samples seem never to start with a syncframe.
This could result in playback of TrueHD streams getting stuck after seeking
because we could never read a syncframe at the start of a sample to determine
the sample size.
Instead of expecting to find a syncframe at the start of a sample, search for it
within the sample, to fix this issue.
Note: this means that we may search a few thousand bytes to find the sample
size, but the cost is only incurred for the first audio sample read.
Issue: #3845
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=191775779
