The extension is .txt, and this is a valid extension for subtiles.
LE: If you have this option enabled and in the folder you have a file with a valid subtitle extension, but the file isn't in fact a subtitle, BSPlayer hangs up with no error message. It does not detect that the subtitle file it's not what it claims to be. I think you can post this as a bug, in the apropiate section: better detection of the corrupted subtitle file (that counts for a non-subtitle :roll: subtitle file)