The behavior's mechanism — pin one track from buffer ground truth, derive one
shared offset, stamp every track onto it — is format-neutral; only the offset
source (PDT) is live-specific. Rename it and its published signal (liveAnchor →
presentationAnchor, matching the PresentationAnchor type it holds) so the name
reflects the general role, and note the non-zero-PTS reuse path through the
existing resolveBufferedAnchor seam. No behavior change.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Rework live anchoring around a single shared anchor established only from
authoritative buffer ground truth, dropping the unreliable manifest estimate:
- anchorLiveTracks establishes the anchor once per source from the first
actually-buffered A/V track (the buffer actor's `initTrackId`, not the
selection), stamps it onto every track via `positionAllTracksToAnchor`
(resolved tracks shift; not-yet-resolved shells get `startDate` for the
parser's `placeOnAnchor`), and publishes it as `liveAnchor`.
- seekToLiveEdge gates its live-edge seek on `liveAnchor`: with no estimate the
pre-anchor window is the raw one, and seeking there would strand the playhead
when the pin later shifts the window. Gating holds the seek until the timeline
is anchored, so it targets the final native-PTS window. (Smoke-tested on Mux
LL-HLS: single seek to the live edge after the pin, clean startup.)
- The resolveBufferedAnchor seam becomes `(deps) -> { trackId, segmentId,
actualStart }`, reading the buffer actor directly (video-first).
An intermittent ~2 s audio model-`startDate` offset (buffers stay aligned, so
playback is synced) remains, tracked as a separate startup race.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Convert anchor-live-tracks from N per-track buffer pins to a single
shared (media-time <-> PDT) anchor applied to every selected track —
video, audio, and now text. A two-state reactor (unanchored -> anchored)
positions from the manifest estimate until a selected A/V track has
SourceBuffer ground truth, then establishes the shared anchor once
(first track to buffer wins) and positions each track onto it by PDT,
leaving it to the parser's carry-forward thereafter.
The resolveBufferedAnchor seam now takes the standard (track, deps)
setup arguments instead of closing over engine scope; the HLS engine's
implementation lives in its own generic module (resolve-buffered-anchor)
so a future audio-only-live engine can reuse it. anchorLiveTracks is now
a makeAnchorLiveTracks<Context>() factory mirroring makeShareSignals.
Realizes internal/decisions/live-presentation-anchor.md.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Capture the decision to hold one rolling (media-time ↔ PDT) anchor — learned
from the first A/V track to obtain SourceBuffer ground truth and applied to all
selected tracks (incl. text) by per-segment PDT — replacing today's per-track
buffer pins, which are redundant under the no-skew assumption and can't anchor
text (no SourceBuffer). New decision doc live-presentation-anchor.md; resolves
the deferred single-rolling-anchor question in live-timeline-anchoring and
promotes [4] in live-presentation-modeling to presentation-level.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Two decision docs for the live-HLS timeline work:
- mse-timestamp-offset — native-PTS default for live; timestampOffset reserved
for relocation (the manifest→buffer / encoded layer).
- live-timeline-anchoring — align demuxed tracks and recover turnover via PDT,
not sequence number (the manifest layer).
Resolve open questions [4] (sync anchor) and turnover startTime recovery in
live-presentation-modeling, pointing at the decisions.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
