fallbackEncoding

The encoding an external subtitle file is read in when it has no byte-order mark and is not UTF-8, in place of a guess from its bytes (#515). Null guesses.

This is the standing preference a player's settings offer, as VLC's default subtitle encoding and mpv's sub-codepage are: a UTF-8 file, which most files now are, is still read as UTF-8. SubtitleSource.encoding is the other strength, a choice for one file that is used whatever its bytes say. The names are SubtitleSource.ENCODINGS and the labels for them. A file read this way raises no PlaybackWarning.SubtitleCharsetGuessed, because nothing was guessed. An East Asian encoding the backend has no table for leaves the guess to decide.