fix(preview): stop re-seeking the native view at every cut and in speed regions - #977
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📝 WalkthroughWalkthroughCompositor frame packets now include clip and source-time positions. The native preview publishes this metadata, maps it to programme time, and uses reported position to coordinate clip changes and playback drift correction. ChangesNative Preview Position Sync
Priority: ⬇️ Low Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix Sequence Diagram(s)sequenceDiagram
participant useNativeCompositorView
participant nativeSync
participant NativeCompositorOverlay
participant NativeCompositorView
useNativeCompositorView->>nativeSync: publish frame position
NativeCompositorOverlay->>nativeSync: calculate native lead and check drift
nativeSync-->>NativeCompositorOverlay: return resync decision
NativeCompositorOverlay->>NativeCompositorView: call setActiveClip when resync is requested
Merge Risk: 🟡 Moderate · up to During native preview playback, a stalled view can go uncorrected. Inside speed regions, drift detection can use the wrong rate. With older native binaries, jumping within the same clip while playing leaves the preview at its old position. Fix these before merging. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The inspected changes do not expand access to files or grant new privileges. The main concern is that playback positions lack project identity, so replacing a project that uses the same primary recording can leave the preview following the previous media selection. Retained concerns
Security review detailsSecurity Blast Radius
Trust Boundaries and Controls
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🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 18 functions across 12 files. (1 skipped: 1 unsupported.)
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…ed regions While playing, the native view runs its own clock and crosses clip boundaries by itself, preloading the next clip ahead of the cut. Two things kept steering it anyway: - The overlay re-sent the clip at every cut, with a pause around it. The view then sought back to a place it had already passed, or threw away the clip it had preloaded and opened it synchronously: a hitch at every cut, which on a transcript-edited take means every few seconds. - The playback sync guessed drift from the wall clock at 1x speed. Inside a 2x speed region that guess was 100 ms off every 100 ms, and the view was re-seeked about ten times a second. Every frame now carries where the view was when it composed it (clip index, source time, both transports). The overlay compares that with the playhead on the trim-compressed programme timeline, where a cut is no jump: a cut crossed in play is left to the view, a jump is followed at once, and a gap over 150 ms that holds for 100 ms re-anchors the view, at most every 500 ms. The wall-clock guess is gone. An addon that reports no position is driven as before.
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Actionable comments posted: 2
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Inline comments:
Review comments at @src/native/nativeSync.ts:
- Line 69: Update nativeLeadSec and programmeTimeSec to account for the active
speed region when mapping and extrapolating native positions, and cap
extrapolation so stale frames cannot advance indefinitely. Add a stalled-view
regression case that starts synchronized when publishing stops, verifying
watchDrift detects the resulting drift.
Review comments at @src/native/useNativePlaybackSync.ts:
- Line 61: Restore a fallback correction in useNativePlaybackSync when native
position is unavailable, so a same-clip playback jump still sends a time update
instead of relying on NativeCompositorOverlay’s clip-change handling or
nativeLeadSec drift watch. Add a regression case for a same-clip playback jump
with a position-less addon.
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📒 Files selected for processing (13)
crates/compositor-view-napi/src/lib.rscrates/compositor/src/live.rscrates/compositor/src/shared_frames.rselectron/native-bridge/services/compositorViewService.tselectron/native/compositor-view/addon.d.tssrc/components/ai-edition/NativeCompositorOverlay.test.tsxsrc/components/ai-edition/NativeCompositorOverlay.tsxsrc/native/contracts.tssrc/native/hooks/useNativeCompositorView.tssrc/native/nativeSync.test.tssrc/native/nativeSync.tssrc/native/useNativePlaybackSync.tstechnical-documentation/architecture/preview.md
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…frozen view The drift watch compared programme seconds and aged the last frame at 1x: inside a 16x speed region a view in step looked half a second behind and was re-seeked twice a second, and a view that froze in step with the playhead aged along with it and was never caught. The gap is now divided by the region's speed, and a frame is aged by at most 250 ms. An addon that reports no position gets its wall-clock correction back, so a jump inside the clip while playing still reaches it.
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Summary
While playing, the native view runs its own clock and crosses clip boundaries by itself, preloading the next clip ahead of the cut. Two things kept steering it anyway:
NativeCompositorOverlayre-sent the clip at every cut, with a pause around it. Arriving after the view had crossed, it made it seek back to a place it had already passed (a key-frame seek, ~50 ms measured for the two decoders, and a few frames shown again). Arriving before, it threw away the clip the view had preloaded and opened it synchronously (up to ~120 ms measured). On a transcript-edited take, cuts come every few seconds.useNativePlaybackSyncguessed drift from the wall clock at 1× speed. Inside a 2× region the guess was 100 ms off every 100 ms, and each miss re-seeked the view.The fix measures instead of guessing:
FramePositioninlive.rs).nativeSync.tscompares that with the playhead on the trim-compressed programme timeline, where a cut is no jump.Related issue
None: found during the preview-fluidity investigation behind #975 and #976.
Type of change
Release impact
Desktop impact
Screenshots / video
No visual change beyond smoother playback across cuts and speed regions.
Testing
nativeSync.test.ts(12): programme mapping across a cut, frame ageing, persistence and cooldown of the drift watch, a position-less addon forgotten.NativeCompositorOverlay.test.tsx(5, new): a cut crossed in play sends nothing; a jump re-anchors at once without pausing the view; a stall is re-anchored once the gap holds; a clip change while paused still sends the clip; an addon without positions is still paused across the swap. Reverting the cut rule fails the first test.cargo test --release -p openscreen-compositor --lib --test shared_frame_handoff: 396 + 1 pass.npx vitest --run: full suite green (300 files, 4 138 tests).tsc --noEmit(app and tests), Biome,npm run docs:check.🤖 Generated with Claude Code
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Bug Fixes
Documentation