What is an SRT file ?

The SubRip subtitle format in plain words: what is inside an .srt file, how players read it, the mistakes that break it, and a validator to check yours.

An SRT file (SubRip Subtitle, extension .srt) is a plain-text file that stores subtitles and when to show them. It was created for SubRip, a free Windows program from around 2000 that extracted subtitles from DVDs, and it has outlived that program because it is so simple: no header, no styling, just numbered blocks of timing and text. Today YouTube, Facebook, LinkedIn, Vimeo, Premiere Pro, DaVinci Resolve, VLC and nearly every smart TV read it.

Anatomy of one SRT subtitle: tap each part

1
00:00:01,000 --> 00:00:03,900
The road north was closed.
 
Start time. Hours:minutes:seconds,milliseconds. Two digits each, three for milliseconds, and a comma (not a full stop) before the milliseconds.

The rules of the format

  • Blocks are separated by exactly one blank line.
  • The timing line is HH:MM:SS,mmm --> HH:MM:SS,mmm. The comma before the milliseconds is SRT's signature; WebVTT uses a full stop.
  • Times are measured from the start of the video, not from the previous subtitle.
  • Save as UTF-8 text. Encoding problems cause most “weird characters” complaints.
  • Formatting is limited to <i>, <b>, <u> and, in some players, <font color="…">.

SRT validator

Paste an SRT file to check its structure and readability. Nothing is sent anywhere.

3 subtitles parsed.

Format errors

  • Block 2: timing “00:00:03.200 --> 00:00:04,000” is not strict SRT (HH:MM:SS,mmm --> HH:MM:SS,mmm, comma before milliseconds).
  • Block 3: numbered 4, expected 3.

Readability warnings

  • Subtitle 1: Overlaps next cue by 0.30 s.
  • Subtitle 2: On screen only 0.80 s.
  • Subtitle 2: 68.8 characters/s (over 17).
  • Subtitle 2: Line over 42 characters.

SRT vs VTT vs other formats

FormatLooks likeMain use
SRT00:00:04,120 --> 00:00:07,480Everything: platforms, editors, TVs
WebVTTWEBVTT header, 00:04.120 --> 00:07.480HTML5 video, streaming
SBV0:00:04.120,0:00:07.480YouTube
ASS/SSADialogue: 0,0:00:04.12,…Styled subtitles, anime, karaoke
SCC, STL, TTMLBroadcast codes / XMLTV broadcast and streaming deliveries

Switch between them with the subtitle converter, or go directly SRT to VTT and VTT to SRT.

How to make an SRT file

By hand, open a plain-text editor, type blocks in the format above and save as name.srt with UTF-8 encoding. For anything longer than a minute, generate it: the AI subtitle generator transcribes a video with AI, powered by Vercel AI Gateway, and writes a correctly formatted SRT, which you can then fine-tune in the SRT editor.

Questions people ask

What is an SRT file?

An SRT (SubRip Subtitle) file is a plain-text file that holds subtitles: a sequence number, a start and end time, and the text for each subtitle, separated by blank lines. Video players and platforms read it to show captions in time with a video.

How do I open an SRT file?

Any text editor opens it (Notepad, TextEdit in plain-text mode, VS Code). To watch it with a video, put it next to the video with the same file name and open the video in VLC, or load it in our SRT editor to see it on the picture.

How do I create an SRT file?

Type it by hand in a text editor following the format above and save with a .srt extension in UTF-8, or generate one automatically from a video with the AI subtitle generator on this site.

Why do my SRT subtitles show strange characters?

The file is not saved as UTF-8. Accented letters saved in an old Windows encoding look like é in many players. Re-save the file as UTF-8 (our converter and editor always export UTF-8).

Can an SRT file change the font or colour?

Barely. Some players honour <font color> and <i>/<b>/<u> tags, but font, size and position are chosen by the player. For full styling use ASS, or burn the subtitles into the video.