Switch the Windows FFmpeg download from gyan.dev (single US mirror, ~0.1 MB/s
for the reporter) to BtbN's GitHub build, served via GitHub's CDN. Uses the
pinned asset ffmpeg-n8.1-latest-win64-gpl-8.1.zip and verifies it against
BtbN's combined checksums.sha256 (one file listing every asset), replacing the
old per-file {url}.sha256 companion fetch. Fails closed if the archive is not
listed. Custom STEMDECK_FFMPEG_URL overrides still skip verification.
Also detect a manually-placed FFmpeg under data/ffmpeg/bin/ (the upstream
folder layout) in addition to the flat data/ffmpeg/ location, so users who drop
in their own build are honored instead of triggering a download. Detection now
flows through resolve_existing_ffmpeg across probe_runtime, ffmpeg_dir_if_present,
and ensure_ffmpeg; write_setup_config records ffprobe next to the resolved
ffmpeg.
Tha.Les
ec73f55d48