USF subtitle external file support
USF is a new XML based subtitle format. It will be the future format of choice for Matroska (once the format is finished). It has a lot going for it. It's much nicer defined then things like SSA, yet more powerful than Subrip or MicroDVD.
It deals with character encoding, different languages, different subtitle tracks (i.e. for directors comments), is expandable and easily parsable (in comparison to some other formats like SAMI and SSA). Basically, if developed correctly, it is gonna be the best format out there.
VLC support USF and USF in matroska, but isn't able to read it as a seperate file yet. (like for avi and other filetypes)