What is an SRT file? How subtitle files work, and how to open one
An SRT file is a plain-text subtitle file: numbered captions with start and end times. How to read, open and edit one, and how SRT compares with WebVTT.
hopeengineer · Founder of Sharpy and Threadify18 October 2026 · 6 min read
The short answer
An SRT file is a plain-text subtitle file. It lists each caption with a number, a start and end time, and the words, and a video player shows those words over the video at those times. The file holds no picture or sound, so you can open and edit it in any text editor, and YouTube and most players read it. Sharpy writes SRT and WebVTT files beside your video when you export it with captions, on your Mac.
What does an SRT file look like?
Like this. Each caption is a block of three parts, and a blank line ends the block:
1
00:00:01,000 --> 00:00:03,500
Every decision in this edit
has a reason.
2
00:00:03,900 --> 00:00:06,200
You can read each one.
- The number. Captions are numbered in order, starting at 1.
- The times. Start and end, joined by an arrow, written as hours, minutes, seconds and milliseconds. The comma before the milliseconds is SRT's mark; most other formats use a full stop.
- The words. One or two lines, shown for exactly that stretch.
The name comes from SubRip, a program that pulled subtitles off DVDs into text files. There is no official specification: the Library of Congress describes SRT as "not well standardized", which is why players differ on extras such as italic or bold tags.
What is the use of SRT files?
To keep the words separate from the picture. Because the subtitles live in their own file:
- Viewers choose. They switch subtitles on or off, and pick a language when there are several files.
- Search engines and platforms read the words. A file of text is searchable in a way burned-in words are not.
- Fixes are cheap. A misspelt name is corrected in a text file, with no new render.
- One video serves many languages. Add a file per language instead of a version per language.
How do you open and edit an SRT file?
On a Mac, Control-click the file, choose Open With and pick TextEdit or any code editor. Keep a few rules when you edit:
- Keep the shape. Number, times, words, blank line, for every block.
- Keep the arrow and the commas. The times must stay in the form 00:00:01,000 --> 00:00:03,500.
- Keep the times in order. A caption should end before the next one starts.
- Save as plain text in UTF-8. In TextEdit, choose Format, then Make Plain Text, before you save, and keep the .srt ending.
To watch it with the video, load it in a player that accepts subtitle files, or upload it to the platform with the video.
SRT vs VTT: what is the difference?
WebVTT, the .vtt file, is SRT's younger relative, written for the web by the W3C. The same captions in WebVTT look like this:
WEBVTT
00:00:01.000 --> 00:00:03.500
Every decision in this edit
has a reason.
The file opens with the word WEBVTT, the milliseconds follow a full stop, and the numbers are optional. Beyond that, WebVTT can place a caption on the screen, style it with CSS and carry comments, which SRT cannot. A third format, SCC, carries US broadcast closed captions.
| SRT | WebVTT | SCC | |
|---|---|---|---|
| Who defines it | Nobody formally; it grew from SubRip | The W3C, as a Candidate Recommendation Draft | US broadcast practice, for 608 captions |
| Times written as | 00:00:01,000 | 00:00:01.000 | Broadcast timecode in frames |
| Position and style | Basic tags, read by some players | Placement, alignment and CSS styling | 608's fixed grid |
| Readable in a text editor | Yes | Yes | The words are stored as codes |
| Best for | YouTube, editors and almost any player | Web video players | Television and platforms that ask for 608 |
To turn an SRT into WebVTT by hand, add WEBVTT and a blank line at the top and change each time's comma to a full stop; the caption numbers can stay, because WebVTT reads them as names for the cues.
Burned-in captions or a separate subtitle file?
Both have a place. Burned-in captions, also called open captions, are part of the picture: every viewer sees them, styled and animated exactly as you made them, which is why shorts use them. A side-car file such as SRT can be switched off, translated and corrected, but each player draws it in its own plain style. Many videos carry both: animated captions on the picture, and a file for search, translation and viewers who prefer their own.
How do you upload an SRT file to YouTube?
YouTube's help gives these steps:
- Open YouTube Studio and choose Subtitles from the left menu.
- Choose the video, then click Add language and pick the language.
- Under Subtitles, click Add, then choose Upload file.
- Choose With timing, then Continue, and select your SRT file.
- Click Save.
YouTube reads only basic SRT: its help says no style markup is recognised and the file must be plain UTF-8.
How does Sharpy make SRT files?
From the captions themselves, on your Mac. Tick the captions box in the export panel and Sharpy writes SRT and WebVTT files beside the finished video, after the render succeeds. They are written from the captions on the picture rather than the raw transcript, so a word you corrected by hand is corrected in the files too. Each caption breaks where the sentence ends, its lines are balanced rather than filled to the edge, and it stays up at least as long as it is read. Translated languages get their own files, named by language.
Sharpy also puts the words inside the movie as a subtitle track per language, so players show them without a separate file. And it checks subtitle files, its own or anyone's: check_captions holds an SRT or WebVTT file to the published rules of Netflix, Prime Video, the BBC, DCMP or ESIST and names every caption that breaks one. Closed captions, subtitles and SDH covers those rules, and captions on your Mac covers every kind of caption Sharpy makes.
Frequently asked questions
01What is an SRT file and how do I open it?
A plain-text subtitle file of numbered captions with start and end times. Open it in TextEdit or any text editor to read or change it, or load it in a video player to see it over the video.
02Is an SRT file safe?
Yes, in itself: it is plain text and cannot run anything. The risk is a file pretending to be one, so check the full name ends in .srt and not, say, .srt.exe (turn on Show all filename extensions in Finder's settings), keep your player up to date, and take subtitles only from sources you trust.
03What is the use of SRT files?
They carry subtitles separately from the video, so viewers can switch them on, choose a language, and platforms can read the words.
04Is an SRT file a subtitle file?
Yes. SRT is the most widely read subtitle format, used for subtitles and captions alike.
05Can I convert SRT to VTT?
Yes. Add WEBVTT at the top and change the commas in the times to full stops. Sharpy writes both formats at once.
Sources
Checked on 18 October 2026.
Written by
hopeengineer
Software architect and founder of Sharpy and Threadify. Builds scalable systems and AI tools, and writes here about how Sharpy understands and edits video.
Sharpy opens on 1 November 2026.
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