Supported subtitle formats

Is there any way to enable .sub -subtitle files in AppleTV ? So far I have only used .srt format, but those
are just a minor part of all subtitles translated to finnish language. I have tried different sub to srt converters
but those usually don’t work like they should.

I guess it’s a Perian related question, but as far as I understood, they are not going to provide .sub support.