# Packet F — synthetic movie-with-sound

Helios, 13 September 2026. Branch `cursor/astra-gates-0101`.

No FFmpeg permission. No ProRes claim.

## Encoder decision

WebM SimpleBlock timecodes are signed int16 relative to Cluster Timestamp, so a single cluster at 0 clamps at **32.767s**. The muxer in `src/lib/korgi/mux-webm-av.ts` starts a new cluster before the relative timecode would overflow.

Audio is **Matroska `A_PCM/INT/LIT`** at 48 kHz. WebM-strict players may ignore PCM (they expect Opus/Vorbis). This is the bounded proof that picture and a known click track share timestamps past 32.767s.

| Claim | Label |
|---|---|
| 10s picture + click track | **passing** (`mux-webm-av.test.ts`) |
| Export longer than 32.767s | **passing** (34s, `maxAbsMs > 32767`, ≥2 clusters) |
| Shared evaluator as frame source | `renderFrame` / `drawingForEvaluatedFrame` on the Packet B fixture |
| Studio “Export movie” GUI | still WebCodecs video-only when the browser has an encoder |
| Opus / FFmpeg / ProRes | **not claimed** |

Tests write `docs/oss/packet-f/packet-f-10s.webm` and `packet-f-34s.webm` locally. They are regenerable; Drive remains the durable park if those binaries need to ship with a handback.