# A small FFmpeg for johnmcm.com

The engine behind https://johnmcm.com/dav-to-mp4 and
https://johnmcm.com/dss-to-mp3: FFmpeg 5.1.6 and LAME 3.100 compiled to
WebAssembly with only what those two pages need. It is served from
`/vendor/local/ffmpeg@1/` and runs in its own worker, one FFmpeg per
conversion.

## Licence

FFmpeg is built here without `--enable-gpl` and with no GPL libraries, so
it is under the GNU Lesser General Public License 2.1 or later; LAME is LGPL
too. See `COPYING.LGPLv2.1` (copied into the build output). The page loads
the engine as separate files, which can be rebuilt from this folder and
replaced.

## What is in it

- Readers: Dahua DAV (`dhav`), raw H.264 and HEVC, MPEG program and
  transport streams, AVI, MP4/MOV, DSS, WAV, MP3, AAC, G.726.
- Decoders: H.264 and HEVC (only so FFmpeg can read a stream's picture size;
  the pages copy video, never decode it), G.711 A-law and µ-law, PCM, MS
  ADPCM, G.722, G.726, G.729, AAC, MP1/MP2/MP3, DSS SP, G.723.1.
- Encoders: AAC, MP3 (LAME), 16-bit PCM.
- Writers: MP4, MOV, M4A, MP3, WAV.

## Files

- `Dockerfile`: the whole build, in Emscripten 6.0.10 (pinned by digest).
- `source/`: the two release tarballs built from, checked against their
  SHA-256 sums.
- `src/run.mjs`: one run of ffmpeg with an input and a streaming output.
- `src/worker.mjs`: the worker the pages talk to.
- `build.ps1`: downloads and checks the tarballs if missing, runs the
  Docker build and copies the result to `frontend/vendor/local/ffmpeg@1/`.