Allow external subtitle files (SRT, ASS, PGS, etc.) to be muxed into
MKV output containers when the device profile requests Embed delivery.
Previously, the IsExternal guard in GetSubtitleProfile excluded external
subtitles from Embed consideration entirely, forcing them to be served
as separate sidecar files even when the output container supports
embedding.
Changes:
- Extract CanConsiderEmbedSubtitle in StreamBuilder to allow external
subs through when transcoding to MKV
- Add external subtitle file as FFmpeg input (-i) for Embed delivery
- Map external embedded subs from the correct FFmpeg input index
- Fix external audio map index to account for the new subtitle input
- Extract NeedsExternalSubtitleMuxing in EncodingHelper to deduplicate
the external subtitle input check
Fixes#16403
2a689f268b