Subtitles (srt, sub, sbv)
SubRip is the native subtitle format of the SubRip program. It is one of the most used formats for subtitles, supported by most software video players, many subtitle creation/editing tools and some hardware home media players. YouTube also supports .srt files.
An entry in a .srt file may contain certain HTML tags, like
SubViewer files (.sub) are the native subtitle format of the SubViewer utility.
.sbv is the file format outputted by YouTube's Automatic Timing feature which creates automatically timed captions based on a transcript