EBU STL is a binary file that web players and most consumer apps cannot read. MCC is accepted by broadcast delivery specifications and caption tools that need frame-accurate caption packets. EBU-STL is at home in subtitles delivered to European broadcasters; MCC is the usual choice for closed captions for broadcast and streaming delivery that carry CEA-708 as well as CEA-608.
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. Only Latin-alphabet EBU STL files are read. Colours, boxes and double-height text are dropped; italics, underline, line breaks, position and justification are kept, and times are shifted back by the programme start the header declares. 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.