What is an SRT file?

Short answer

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.

Related answers
SRT vs VTT — which format should I use?

SRT for almost everything: video editors, YouTube, Vimeo, every major platform. VTT only when you're embedding video on a website with HTML5 <track>.

Full reference
SRT glossary entry — history, cue syntax, and styling caveats in depth.
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