Close the recurring "video has subtitles but the web player shows none" gap
with a source-agnostic pipeline:
- Discover EXTERNAL sidecar subs in the scan (Video.es.ass siblings + a Subs/
bundle), parse lang/forced/SDH from the filename, skip VobSub (.sub+.idx).
ffprobe-only scanning ignored these (ToonsHub/anime "MSubs" releases).
- Transcode sidecar charset -> UTF-8 before WebVTT (BOM/UTF-16/code-page by
language). Chinese SCRIPT matters: chs/sc -> GBK, cht/tc/big5 -> Big5
(decoding one as the other is mojibake).
- /sub now serves a standalone sidecar file (i=-1, p=file, &l=lang hint) and a
remote debrid URL (ffmpeg reads http, no local stat) — not just embedded
streams of a local file.
- probe.json emits a tokened vttUrl per TEXT track so torrent/debrid HLS streams
(never library-scanned) get subtitles too. Embedded index is counted among
embedded streams only, so -map 0:s:N stays aligned when sidecars are appended.
Tested against a real 347-file gallery: 26/26 sidecars and embedded ass/srt/
mov_text all extract to valid WebVTT; bitmap (pgs/dvd_subtitle) correctly stays
burn-in. Manual harness gated behind GALLERY_DIR.
