SubToolbox

What Is an SRT File? The Format, Explained

SRT — short for SubRip — is the format subtitles travel in almost everywhere: YouTube uploads, VLC, Premiere Pro, TV players, course platforms. Its success is its plainness: it is a text file you can open in Notepad, with no header, no styles and no mystery. This page dissects one block by block.

Quick answer: An SRT file stores subtitles as numbered plain-text blocks — an index line, a start --> end timestamp with comma milliseconds, the caption text, and a blank line — with no styling and no header. Virtually every player and editor reads it.

The anatomy of one block

Repeat that block for every subtitle and you have a complete SRT file — nothing before the first block, nothing after the last.

  • Line 1 — the cue number: 1, 2, 3… (sequential, but most parsers don't enforce it)
  • Line 2 — the timing: 00:00:01,000 --> 00:00:04,500 (hours:minutes:seconds,comma milliseconds)
  • Line 3+ — the caption text: one or two lines, shown exactly as written
  • A blank line — the separator before the next block

Where it came from

SubRip was a Windows program from the early 2000s that ripped DVD subtitles into this minimal text form using optical character recognition. The format it wrote outlived the program by two decades: the simplicity that made it easy to write made it easy to read, and "an SRT file" became the default meaning of the word subtitle.

What SRT deliberately lacks

No fonts, colours, positioning or effects — the format cannot express them, which is why styled formats like ASS exist alongside it. No header or metadata either: a file that begins with anything other than the first cue number is technically already invalid, though tolerant parsers (including the ones on this site) forgive leading whitespace or BOM marks.

Who reads SRT

  • YouTube — upload under Subtitles, or add as a caption track
  • VLC, MPV, MPC-HC and most desktop players — auto-load when named like the video
  • Premiere Pro, DaVinci Resolve, Final Cut — import as caption tracks
  • HTML5 web players — via conversion to WebVTT (the browser standard)

Frequently Asked Questions

Are SRT files just text files?
Yes — with a specific layout. You can rename a .txt to .srt, but unless the content follows the numbered-block pattern with valid timestamps, players will reject or misread it. The reverse also holds: an SRT opens happily in any text editor.
What does the comma in 00:00:01,000 mean?
It separates seconds from milliseconds — SRT's convention. WebVTT writes the same value with a dot: 00:00:01.000. Mixing the two is the single most common cause of a "valid-looking" file not loading.
How big is a typical SRT file?
Small: a feature film's subtitles are typically 50–150 KB of text regardless of video length, because only the words and numbers are stored.
Do SRT files expire or stop working?
No — as plain text they are as durable as any text file. Player support has only widened over the format's twenty-plus years.

More tools used in this guide

SRT Viewer & Quick Fix
Open SRT or VTT and read it as a clean cue table — with one-click fixes for overlaps, numbering, tags and reading speed.
SRT Converter
Convert between SRT, WebVTT, ASS, SBV and plain text. The file is parsed in your browser — nothing is uploaded.
SRT File Generator
Build an SRT file from scratch — add cues with start, end and text, validate as you type, download a clean .srt.

More guides

SRT vs VTT
The two formats compared: header, millisecond separator, styling and where each one is required.
How to Make an SRT File
Four honest ways to create an SRT — build it, convert it, transcribe-and-time it, or generate one from text.