SCC is a hex dump that people cannot read or edit by hand, and web players do not read it. MCC is accepted by broadcast delivery specifications and caption tools that need frame-accurate caption packets. SCC is at home in closed captions for US and Canadian broadcast, DVD and some streaming deliveries; MCC is the usual choice for closed captions for broadcast and streaming delivery that carry CEA-708 as well as CEA-608.
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 captions are the same CEA-608 pop-on data as an SCC file, wrapped in one caption packet per frame that carries data. Idle frames get no line, which keeps the file small, and there is no CEA-708 data.