Caption retiming and Sequence clocks: small tested examples for agent-driven edits

[the-media-vampire]

I maintain Veyrul, a saved media-knowledge service for agents, and built two small local examples for agents working in Remotion. I'm looking for a real edit to test the limits against, not asking anyone to adopt a new renderer.

1. Captions after cuts, repeated clips and rational speed changes. The subtle bug was rounding twice: 11/3 seconds rounded to 3,666,667 microseconds puts a boundary just after frame 110 at 30 fps. The adapter derives frame boundaries from retained source/cut identities before frame rounding. Code, inputs, commands and limits.

2. Composition-timed captions inside a Sequence. A Sequence starting at frame 24 sees local frame 0 there. The helper converts and clips global intervals instead of retiming the source again. A later controlled reuse caught an additional condition: for nested Sequences, intersect every ancestor's active window; summing offsets alone is insufficient. Small helper and exact scope.

Our checks used Remotion 4.0.537 on macOS arm64: two silent diagnostic edits, 351 decoded frames checked for source timing/caption visibility, 18 caption OCR samples, and 13 rendered Sequence-boundary stills. These are founder-controlled checks, not customer results, speech-sync validation or proof for arbitrary footage. The initial capture-path failure is retained in the example's TESTED.json.

Veyrul's part is finding the saved code/evidence before editing. The agent still uses normal Remotion APIs and runs locally. Public lookup needs no Veyrul account/key; no source footage or private transcript needs uploading. Existing MCP clients can use https://veyrul.com/mcp/read; ask get_context for word captions retime cuts speed changes, detail="compact", limit=3. The code can also be inspected and used directly without connecting. Remotion's own license terms still apply.

If you or your agent are already working on a relevant edit, a public-safe timing map, constraint or failing boundary would be useful. I'll help check whether the saved resource applies and record misses as well as useful results; please keep private transcripts/media out of the thread. For context, #12927 is the separate existing resources-list suggestion, not a request to change Remotion itself.