SCC is a hex dump that people cannot read or edit by hand, and web players do not read it. SRT is accepted by practically every player, site and editor. SCC is at home in closed captions for US and Canadian broadcast, DVD and some streaming deliveries; SRT is the usual choice for subtitles that must work almost everywhere.
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. Positioned lines are written with {\an} codes, which many players honour; players that do not simply show them at the bottom.