Assets whose A/V encode starts at a non-zero native PTS (Mux instant clips,
Apple bipbop @10s) are relocated onto a 0-based presentation timeline via
`SourceBuffer.timestampOffset`, so buffer / model / `currentTime` / `seekable`
stay 0-based and the adapter is untouched.
- `establishStartMediaTime` reactor establishes each track's media-timeline
origin once per source (the DOM-free half), running an injected
`deriveStartMediaTime` seam over discovered container data.
- Default `deriveSharedMinStartMediaTime`: relocate every track by the `min`
across selected A/V origins — preserves real A/V skew and keeps every DTS >= 0.
Origins below NEAR_ZERO_ORIGIN_THRESHOLD (1s) are left native (ordinary
~0-PTS VOD isn't perturbed).
- `relocation-steps` message pipelines discover the origin (mdhd/tfdt head-peek)
and stamp `timestampOffset`; text cues rebase by X-TIMESTAMP-MAP − origin.
- Wired into both the default and audio-only HLS engines.
See internal/design/spf/presentation-timeline-model.md.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
