SBV is understood mainly by YouTube and a few caption tools. EBU STL is the file European broadcasters ask for when subtitles are delivered with a programme. SBV is at home in uploading and downloading YouTube captions; EBU-STL is the usual choice for subtitles delivered to European broadcasters.
The text is read as UTF-8 or UTF-16, whichever the file is. An older file in another code page is read using the charset it declares, or as Windows-1252 if it declares none, so accented letters in an unlabelled legacy file can come out wrong. A file that is not text, such as the picture-based subtitles of a DVD, is refused instead of being converted to nonsense. Of the styling, only italic, bold, underline and the position on screen (top, middle or bottom, left, centre or right) travel between formats; fonts, colours, outlines and effects do not. The file is written as STL25.01 in the Latin character set, 25 frames per second, with italics, underline, line breaks, position and justification. Characters outside the character set become a question mark.