MCC is a hex dump that most players, and people, cannot read. TTML is accepted by broadcast and streaming platforms. MCC is at home in closed captions for broadcast and streaming delivery that carry CEA-708 as well as CEA-608; TTML is the usual choice for subtitles delivered to broadcasters and streaming services.
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 CEA-608 caption data inside each packet is read, as for SCC. Captions that exist only as CEA-708 service data are not read. Positions are written as TTML regions and italic, bold and underline as styled spans; the result is a plain TTML file with no broadcast-specific profile.