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Miguel Angel Simon Sierra
deb351a8cf
The runtime re-derived the composition's total duration on every animation
frame. transportTick called getSafeTimelineDurationSeconds unconditionally,
and deriving it scans every media element in the document and walks each
one's composition ancestry to resolve an absolute start and duration.
That value is a function of the composition, not of the playhead, so a
paused editor with nothing happening recomputed the same answer ~60 times a
second. On a 91-media-element composition the media scan ran 1.05 times per
frame while the editor sat idle and untouched.
Derive it once and reuse it until an input could have changed. The inputs,
and the signal that catches each:
- timing attributes edited (live editing, variables re-applied, the
runtime's own autostamping) -> MutationObserver with an attribute filter
- timed elements added or removed, including nested compositions that
mount asynchronously after init -> the same observer, childList+subtree
- media metadata arriving, or el.load() resetting duration to NaN, neither
of which mutates the DOM -> capture-phase media event listeners
- a timeline registered or lengthened in window.__timelines, a plain
object nothing can observe -> a registry signature compared on read
Observer records are delivered in a microtask, so the queue is drained on
read as well; otherwise an edit read back in the same synchronous block, the
ordinary live-editing case, would be served the pre-edit value.
The render path does not read the cache at all. Capture depends on the exact
duration and a frame rendered against a wrong one cannot be recovered, so it
pays the full derivation on every frame exactly as before.
Measured on the 91-media-element composition, idle and untouched: media
scans per frame 1.05 -> 0.05. Across 100 single-frame seeks: 2.28 -> 0.11
per seek, so seeking does not invalidate the cache either. The residual is
a separate per-20-tick caller in timeline.ts, untouched here.