What Is an SRT File? How Subtitle Files Work and How to Add Them

An SRT file is a plain text file that holds subtitles. Each subtitle has a number, a start and end time, and the line or two of text to show on screen. Video players read the file alongside the film and display each line at the right moment. Because it is just text, an SRT file is tiny, opens in any text editor and works with a very wide range of players, TVs and editing programs.

The name comes from SubRip, an early program for pulling subtitles off discs. The format outlived the program because it is so simple.

What is inside an SRT file?

Open one in a text editor and you will see blocks like this, separated by blank lines:

• A sequence number, counting up from 1.
• A timecode line such as 00:02:14,500 --> 00:02:17,200: hours, minutes, seconds and milliseconds, with a comma before the milliseconds.
• One or two lines of text, sometimes with simple tags for italics.
• A blank line to end the block.

That is the whole format. There are no fonts, colours or positions beyond the basics; the player decides how the text looks.

Three ways to add subtitles to a movie

1. Use a sidecar file

This is the quickest route. Put the SRT in the same folder as the video and give it exactly the same name, changing only the extension: holiday-2019.mp4 and holiday-2019.srt. Most desktop players and many smart TVs reading from a USB stick will pick it up automatically. If not, look for a Subtitles or Add subtitle file option in the player's menu. For several languages, players often recognise a language code before the extension, such as holiday-2019.en.srt.

2. Add soft subtitles inside the file

Free video tools can combine the video and the SRT into one file without re-encoding the picture. The MKV container handles SRT tracks directly; MP4 can carry text subtitles but usually converts them to its own subtitle format. The advantage is one tidy file with a subtitle track the viewer can turn on or off.

3. Burn the subtitles in

Video editors and converters can render the text onto the picture. Use this when a platform or device will not show separate subtitle tracks, or for short clips shared on social media. Since the video is re-encoded, there is a small loss of quality, and the subtitles can never be removed, so keep a clean copy.

How to fix subtitles that are out of sync

Timing problems come in two kinds, and they need different fixes.

1. Constant offset. Every line is early or late by the same amount, often because the subtitles were made for a version with a different intro. Most players have a subtitle delay control; nudge it until the lines match, then use a subtitle editor to shift the file permanently.
2. Growing drift. Lines start in sync but slide further out as the film goes on. This usually means the subtitles were timed for a different frame rate, for example a 25 frames per second release against a 23.976 version. Subtitle editors have a frame rate conversion that fixes the whole file at once.
3. A gap in the middle. If one scene is cut or added, sync the file in two parts: before and after the change.

Strange characters instead of accents

If letters such as é, ü or ñ appear as random symbols, the file is in a different text encoding from the one the player expects. Open it in a text editor and save it again as UTF-8. Most modern players and TVs handle UTF-8 correctly.

SRT compared with other subtitle formats

• VTT (WebVTT) looks very similar but begins with a WEBVTT header and uses a full stop before the milliseconds. It is the usual format for video on web pages, and it supports positioning.
• ASS and SSA allow fonts, colours, positions and effects, which is why fan-made anime subtitles often use them.
• Image-based subtitles from DVDs and Blu-rays store each line as a picture. They cannot be edited as text without character recognition.

Converting from SRT to VTT is simple; going from a styled format to SRT keeps the words and drops the styling.

Where subtitles fit into a film night

Subtitles open up films in other languages and help in noisy rooms or when someone is asleep next door. They also matter in homes and countries where several languages are spoken, a theme in our piece on viewing for multilingual audiences in Belgium. Use subtitle files that come with a release, ones you have the right to use, or ones you write yourself for home videos. If you are still deciding what to watch, try our method for picking a movie without scrolling all night, and if a file refuses to play at all, the cause is usually covered in what is a video codec.