Someone has sent you a file ending in .srt, or an editor has offered to export one, and you’re not sure what to do with it. Maybe you tried to attach it to a TikTok or a Reel and found nowhere to put it. That’s expected. An SRT is a simple and very useful file, and it helps to know which places are built to read it.
The short answer. An SRT file is a plain text file that holds subtitles: each line of text gets a number, a start time and an end time. A video player reads it alongside the video and shows each line at the right moment. Long-form platforms like YouTube and Vimeo accept SRT uploads, but short-form apps such as TikTok, Instagram Reels and YouTube Shorts take a single video file, so captions there need to be part of the picture.
What’s inside an SRT file
SRT stands for SubRip Text. The name comes from SubRip, an old Windows program that pulled subtitles off DVDs and saved them in this format. The format outlived the program because it’s so easy to read and write.
Open one in a text editor and you’ll see blocks like this:
1
00:00:01,200 --> 00:00:03,800
This is the first subtitle.
2
00:00:04,000 --> 00:00:06,500
And this is the second.Each block has four parts:
- A sequence number. 1, 2, 3 and so on, in order.
- A timing line. Start and end, written as hours, minutes, seconds and milliseconds, with an arrow between them. Note the comma before the milliseconds.
- The text. One or two lines, usually.
- A blank line. This is what tells the player the block has ended.
That’s the whole format. There’s no header, no font, no colour setting and no official way to say where on screen the text should sit. Some players understand a few basic tags such as <i> for italics, but support varies from one player to the next.
Why the format is so widely used
Its simplicity is the point. Because an SRT holds only words and timings, almost any software can read it, and you can fix a typo in any text editor without touching the video.
It also keeps the text machine-readable. A platform that accepts an SRT can show it as a caption track viewers switch on and off, index the words for search, and offer it to translation tools. That’s the closed-caption side of the story, which the post on open vs closed captions covers in more detail.
Where SRT files work
At the time of writing, these all accept an SRT:
- YouTube. In YouTube Studio, the Subtitles section lets you upload a file for a video.
- Vimeo. You can upload a subtitle or caption file for each video.
- Desktop video players. VLC and most others load an SRT that sits next to the video with the same file name.
- Desktop editors. Premiere Pro, DaVinci Resolve and Final Cut Pro can import SRT files to place captions on a timeline, and export them.
SRT and VTT
You’ll often see WebVTT (.vtt) mentioned in the same breath. It’s the web’s version of the same idea. The structure is almost identical, with three visible differences: the file starts with a WEBVTT line, the milliseconds follow a full stop instead of a comma, and each cue can carry settings for position and alignment. If a platform asks for one and you have the other, converters handle it in seconds.
How short-form apps handle captions
Short-form platforms are built around posting one finished video from a phone, and their upload screens reflect that. At the time of writing, the TikTok and Instagram apps don’t have a step for attaching a subtitle file to a video or Reel. Each offers its own auto-generated captions instead, which the platform creates after upload, styles in its own way and lets viewers switch on or off.
YouTube Shorts sits in between. A Short is a YouTube video, so YouTube Studio in a browser can attach a subtitle file to it, but the phone upload flow doesn’t include that step at the time of writing. The subtitles for YouTube Shorts page explains why most creators burn their own in anyway.
That’s why short-form captions are usually burned in. When the text is rendered into the frames, the video carries its captions to any app, in exactly the font, size, outline and position you chose. A muted viewer scrolling past sees the words immediately, with nothing to switch on. The guide to burn subtitles into a video on iPhone compares the two approaches side by side.
Using SRT and burned-in captions together
You don’t have to choose one for every video. The two do different jobs, and plenty of creators use both:
| Where the video goes | What to use |
|---|---|
| TikTok, Reels, Shorts | Burned-in captions, styled for a phone screen |
| YouTube long-form, Vimeo | An SRT upload, plus burned-in captions if you want a set look |
| A client or broadcaster | Whatever their spec asks for, which is often SRT |
| Your own website | A VTT track, so the text stays searchable |
If you post the same clip to several places, burned-in captions travel with it everywhere, and a caption track on the platforms that take one adds search and accessibility controls on top.
Getting the timing right, whichever you use
What makes an SRT good is the same thing that makes burned-in captions good: accurate words and sensible timing. A few things help:
- Keep lines short. Two short lines read faster than one long one.
- Leave no gaps mid-sentence. If one line ends at 3.8 seconds and the next starts at 4.0, the screen flickers empty in between. Joining them up reads more smoothly.
- Avoid overlaps. Two blocks with overlapping times can show on top of each other in some players.
- Save as UTF-8. It keeps accents and non-Latin scripts displaying correctly.
- Check names and jargon. Automatic transcription handles everyday speech well and benefits from a quick read-through for proper nouns.
In Capster, each caption line works much like an SRT block: tap a caption and the editor shows its text and a Timing section with Start and End, which you can nudge or set to the playhead. The difference is what happens on export. Capster renders those lines into the frames in the style you picked, so the video lands in your camera roll ready to post. The steps to add captions to a video on iPhone walk through it from import to export.
Once you know what’s in an SRT, you can tell at a glance where it belongs: a caption track for the platforms that read one, and burned-in text for the feeds where people scroll on mute.