UnheardHits audio import — third-party software notices

The audio importer uses locally hosted, unmodified FFmpeg WebAssembly files.

@ffmpeg/ffmpeg 0.12.15: MIT License, Copyright (c) 2019 Jerome Wu.
License: /vendor/ffmpeg/LICENSE-MIT.txt

@ffmpeg/core 0.12.10 (single-thread): GPL-2.0-or-later, as declared by its
upstream package. FFmpeg and its compiled libraries retain their respective
copyrights. License copies: /vendor/ffmpeg/GPL-2.0.txt and GPL-3.0.txt.
This software is provided without warranty, including merchantability or
fitness for any particular purpose, as specified in those licenses.

Source code and build materials:
https://github.com/ffmpegwasm/ffmpeg.wasm/tree/71aa99d37c02a7b4c435275ca9ef50e612f6efa1
The upstream wrapper/core build source is also provided locally:
/vendor/ffmpeg/source.tar.gz
/vendor/ffmpeg/Dockerfile.upstream
/vendor/ffmpeg/Makefile.upstream

The Dockerfile identifies the upstream FFmpeg source and every external
library source URL/ref used by the core build. These include FFmpeg n5.1.4
(https://github.com/FFmpeg/FFmpeg/tree/n5.1.4), LAME, x264, x265, libvpx,
Ogg, Theora, Opus, Vorbis, zlib, WebP, FreeType, FriBidi, HarfBuzz, libass
and zimg. Their source repositories and dependency build scripts are linked
by the supplied Dockerfile and included build/ directory.

Build instructions:
1. Download/extract source.tar.gz, or clone the upstream repository and
   check out commit 71aa99d37c02a7b4c435275ca9ef50e612f6efa1.
2. Install Docker with buildx and GNU Make. The upstream Dockerfile uses
   emscripten/emsdk:3.1.40 and downloads its declared source dependencies.
3. Run `make prd` in that source tree to build the single-thread core.
   Outputs are written to packages/core/dist; make prd-mt is not used here.
4. For the MIT JavaScript wrapper, follow the root package workspace setup
   and run the packages/ffmpeg build script (TypeScript + webpack).
5. In the UnheardHits source tree, `python3 scripts/vendor-audio.py` restores
   the exact published npm artifacts after verifying their pinned digests.

Distribution changes: JavaScript is unchanged. The 32,232,419-byte WebAssembly
file is split losslessly into four static parts to fit the hosting asset
limit. The importer rejoins them before instantiation; manifest.json records
part paths, total size and SHA-256. The source archive above is unmodified.

Official artifact URLs and integrity digests: /vendor/ffmpeg/provenance.json