What is an SRT file?
SRT (SubRip Subtitle) is a plain-text subtitle format with numbered cues and HH:MM:SS,mmm timestamps. It's the most universal subtitle format.
Detail
SRT files are plain text. Each cue is a numbered block: index, start → end timestamp, text. The format dates to the late 1990s SubRip Windows program and stuck around because of how simple it is. Every video editor, media player, and major consumer platform reads SRT natively. The format technically doesn't support styling, but most modern players unofficially recognize HTML-style tags inside cues — don't rely on that for cross-platform delivery. A typical cue: 1 00:00:01,000 --> 00:00:03,500 Hello world. This is a caption.
SRT for almost everything: video editors, YouTube, Vimeo, every major platform. VTT only when you're embedding video on a website with HTML5 <track>.
Subtitles transcribe spoken dialogue. Closed captions also describe non-speech audio (music, sound effects, speaker IDs) and are the accessibility standard.