The LTC card repainted only on server anchors (~4x/s), so the frame
counter jumped in ~7-frame steps. Now the client counts every frame
locally between anchors and re-syncs on each one — frame-accurate and
smooth, with no extra network traffic.
- Server anchors carry ageMs (how old the decoded timecode is) so clients
can pin the anchor to their own clock. ltc-listener reports it while
running; composeLtc passes it through (listener) or derives it (reader).
- Client does exact SMPTE frame<->timecode math (parseTc/tcToFrames/
framesToTc, incl. 29.97 drop-frame minute counting) and advances the
display in a requestAnimationFrame loop at the LTC's own rate.
- Robust when rAF is throttled (backgrounded tab): render() paints the
extrapolated frame at the 4x/s anchor rate too, so the display never
freezes — the rAF loop only refines it to every frame when visible.
- Anchor jitter can't tick the counter backwards (small regressions
clamped; genuine seeks/re-strikes pass); freshness cap stops freewheel
into phantom frames when anchors stop arriving.
Verified: SMPTE math against the encoder over 200k drop-frame frames plus
round-trips; the extrapolation pipeline simulated at 30/25/29.97DF showing
strict +1-per-frame advance and correct DF boundary crossing.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
