Subtitles in Live Streams
There are several ways to transfer these subtitles: picture or text. Text requires device to render with some font in proper place on screen, picture goes with prerendered text.
Most subtitles received from a satellite are included as pictures and Flussonic identifies such a track as DVB subtitle.
Text subtitles from satellite are identified as DVB teletext. HLS has another format of such subtitles and it is called WebVTT.