Video Scribe - WASM build

The compiled WASM is at src/web/assets/core/dist/ and tracked via Git LFS. Rebuild when updating ffmpeg, adding a codec, or changing build flags.

Prerequisites

• Docker with at least 16 GB allocated (28 GB recommended). In OrbStack: Settings → Resources → Memory.
• ~3 GB disk for Docker layer cache.

Build

Run from the ffmpeg-build/ directory inside the plugin:

cd plugins/video-scribe/ffmpeg-build

docker buildx build \
  --platform linux/amd64 \
  --file Dockerfile.video-scribe \
  --output "type=local,dest=dist" \
  --target exportor \
  --progress=plain \
  . 2>&1 | tee build.log

First run: 30–60 minutes. Subsequent runs: 15–20 minutes — codec stages are cached.

After a successful build

cp ffmpeg-build/dist/dist/esm/ffmpeg-core.* src/web/assets/core/dist/
npm run build

Commit the updated files. Craft picks them up on the next request.

Rebuilding only the ffmpeg stages

Use --no-cache-filter when changing ffmpeg flags without touching the codec libraries:

docker buildx build \
  --platform linux/amd64 \
  --file Dockerfile.video-scribe \
  --output "type=local,dest=dist" \
  --target exportor \
  --no-cache-filter emsdk-base,ffmpeg-base,ffmpeg-builder,ffmpeg-wasm-builder \
  --progress=plain \
  . 2>&1 | tee build.log

Dockerfile stages

Stage	What it builds	Cached?
emsdk-base	Emscripten SDK base image + apt packages	Yes
x264-builder	libx264 (H.264 encoder)	Yes
libvpx-builder	libvpx (VP8/VP9)	Yes
opus-builder	libopus (audio)	Yes
aom-builder	libaom 3.4.0 (AV1)	Yes
dav1d-builder	libdav1d 1.4.3 (fast AV1 decode)	Yes
ffmpeg-base	FFmpeg n5.1.4 source + merged libs	Yes
ffmpeg-builder	FFmpeg configured + compiled	Bust to re-run
ffmpeg-wasm-builder	Emscripten link → .js + .wasm + .worker.js	Bust to re-run

Adding a codec library

1. Add a build script to ffmpeg-build/build/<codec>.sh following the existing pattern.
2. Add a FROM emsdk-base AS <codec>-builder stage in Dockerfile.video-scribe.
3. COPY --from=<codec>-builder $INSTALL_DIR $INSTALL_DIR in ffmpeg-base.
4. Add --enable-lib<codec> to the ffmpeg-builder RUN step.
5. Add -l<codec> to FFMPEG_LIBS in ffmpeg-wasm-builder.
6. Rebuild.

Memory

The build uses -j4 in build/ffmpeg-vs.sh to cap parallel compile jobs. Unlimited parallelism (-j) can push past 20 GB and trigger OOM kills. If you see SIGKILL in the build log, lower parallelism or increase Docker’s memory limit.