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feat(mp4): add the rsot box for redundant sample original timing

ISO/IEC 14496-12:2026 Section 8.8.18 adds the RedundantSampleOriginalTimingBox, a traf child that documents that the first sample of a track fragment is a copy of the previous sample and how long that sample has already been presented, and that the fragment's last sample was truncated to fit the fragment and how long it was meant to last.

Its NOTE 1 names the case it is meant for: adaptive streaming where fixed-duration segments are not aligned with variable frame rate media such as text, so a cue that spans a boundary is restated as a duplicated redundant sample. With rsot_elapsed_duration set, that first sample shall carry sample_depends_on=2 and sample_has_redundancy=1, and a receiver that already has the previous sample extends it rather than presenting the copy again.

Both durations are optional and independent, so the box size follows from the flags; decode rejects any other size rather than reading as far as it goes.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

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