SCC is a hex dump that people cannot read or edit by hand, and web players do not read it. SMI can carry several languages in one file for the players that read it. SCC is at home in closed captions for US and Canadian broadcast, DVD and some streaming deliveries; SMI is the usual choice for subtitles for Korean-market players and multilingual files.
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. CEA-608 pop-on, roll-up and paint-on captions on the first caption channel (or the second, if the first is empty) are read; colours are dropped, and a roll-up row becomes one cue that ends when it scrolls off. Times follow the 29.97 fps frame clock, drop-frame or not. The file is written with one language class, and cues that overlap in time are shown together, as SAMI has a single timeline.