reloadExternalSubtitle
Reads an external subtitle track's file again, in encoding, and puts the new reading in place of the old one (#515).
For a viewer looking at garbled letters. PlaybackWarning.SubtitleCharsetGuessed says when a file's encoding was guessed, and an application can offer SubtitleSource.ENCODINGS as a "Text encoding" menu and call this with the one chosen. The file is read in it as it is, with no guess, and a file that is not in it still loads, read as told, so the viewer sees what the choice does. Null decides from the bytes again, as the first read did, which also suits a file corrected on disk since it was loaded, because the file itself is read again.
The track keeps its id, its place in PlayerSnapshot.tracks, and its selection as the subtitle or the secondary subtitle, and playback does not move. A read that fails leaves the track as it was. Works for any external track: one declared in MediaItem.externalSubtitles or one added with addExternalSubtitle. The choice holds for this load of the track: the item's own SubtitleSource is unchanged, so opening the item again reads the file as that source says, and an application that wants the choice to last sets SubtitleSource.encoding.
Throws
when nothing is open, when the media changes before the file is read, or when a later reload of the same track replaced this one.
when track is not an external subtitle track of the open media, when encoding is not one of SubtitleSource.ENCODINGS or a label for one, or when the file cannot be read, cannot be parsed, parses to no cues, or is to be read in an East Asian encoding the backend has no table for; the message says which.