Rework the segment loader's per-message execution into composable step
pipelines (fetch → dispatch by default); relocation injects discover/stamp
steps between them, so loader + SourceBuffer actor stay relocation-oblivious
and Tier 0 imports no relocation code.
- segment-loader: Frame/LoadStep/StepDeps/MessagePipelines, fetchStep/
dispatchStep (deps as 3rd arg), step-runner makeLoadTask + inFlight wrapper.
- source-buffer: drop CreateAppendMeta; keep idempotent timestampOffset guard.
- relocation.ts / origin-discoverer.ts: TRANSITIONAL — slated for rebuild as
the establishStartMediaTime reactor.
WIP checkpoint; outstanding work tracked in
.claude/plans/spf-non-zero-pts-timestamp-offset-spike.md.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Opt-in relocateTimestampOrigin on the HLS engine. The video loader reads
each track's decode-time origin (tfdt baseMediaDecodeTime / mdhd timescale)
from the init + first media segment, then relocates the buffer to 0-based
via SourceBuffer.timestampOffset = -origin, so currentTime/seekable/duration
stay 0-based with no adapter translation. Off by default (zero-PTS VOD pays
nothing).
The established offset is published on the segment-loader snapshot so the
text path can rebase cues onto the same timeline: cueFinal = cueNative +
timestampOffset, where cueNative applies the X-TIMESTAMP-MAP correction
(Apple) or the absolute cue time (map-less Mux, which can't self-derive the
origin and reads the A/V-established one).
Checkpoint before the composition-driven refactor.
