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James Russo
07de7e61ed
## Description PR 1 of 4 in the WebM (VP9) distributed-rendering series. A gating experiment that proves closed-GOP libvpx-vp9 chunks survive `ffmpeg -f concat -c copy` losslessly, so the rest of the stack can ship Path A (concat-copy) rather than the slower re-encode-in-assemble fallback. Two changes: 1. **Closed-GOP VP9 encoder args.** `buildEncoderArgs` now lays `-g <chunkSize>`, `-keyint_min <chunkSize>`, `-auto-alt-ref 0`, and `-cpu-used 2` on libvpx-vp9 when `lockGopForChunkConcat=true`. Mirrors the existing libx264/libx265 branches. The alt-ref disable is load-bearing — libvpx-vp9's default non-displayable alt-ref frames can reach across chunk seams and break concat-copy. `-cpu-used 2` pins the speed/quality tradeoff so chunks encoded on workers with different libvpx-vp9 defaults produce visually consistent output across seams. Default (`lockGopForChunkConcat` unset) preserves the existing in-process VP9 path unchanged. 2. **Concat-copy smoke test** at `packages/producer/tests/distributed/_smoke/webm-concat-copy.test.ts`. Generates 60 PNGs via lavfi `testsrc2`, encodes them as 4 VP9 chunks of 15 frames using `buildEncoderArgs` with `lockGopForChunkConcat=true`, concat-copies via `ffmpeg -f concat -c copy`, then runs three independent verifications: `ffprobe -show_streams`, `ffmpeg -f null -` decode test, and `ffprobe -count_frames`. Each verification surfaces its failure fingerprint in the error message. Smoke test passes 6/6 locally → Path A works; the rest of the stack takes it. Also exports `buildEncoderArgs` from `@hyperframes/engine` so adapters / tests can construct args without re-implementing the contract. ## Testing - [x] `bunx vitest run --root packages/engine src/services/chunkEncoder.test.ts` — 62/62 pass (new VP9 closed-GOP tests included) - [x] `bun test packages/producer/tests/distributed/_smoke/webm-concat-copy.test.ts` — passes - [x] `bunx oxlint` + `bunx oxfmt --check` on all changed files — clean - [x] `bunx tsc --noEmit -p packages/engine/tsconfig.json` — clean 🤖 Generated with [Claude Code](https://claude.com/claude-code)