What is a .sub file?
Subtitle File (MicroDVD or VobSub) · Video · Various · n/a
A .sub file holds subtitles, but in two different forms. It is either a plain-text MicroDVD file that times lines by video frame, or a binary VobSub picture stream that always comes with a matching .idx file. What opens it depends on which kind you have.
What is a .sub file used for?
The MicroDVD kind is plain text, where each line is timed to frame numbers in curly braces, like {100}{200}Hello. You can read and edit it in a text editor.
The VobSub kind is different: it stores subtitles as images (ripped from DVDs) and never travels alone, it always has a partner .idx file that indexes it. You need both files together, in the same folder, for a player to show them.
To tell them apart, open the .sub in a text editor. If you can read the lines, it is MicroDVD; if it looks like binary junk and there is a .idx beside it, it is VobSub.
Either way, players like VLC display .sub subtitles with a video, and subtitle tools can convert them to the simpler, more portable SRT.
What opens a .sub file?
The .sub format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- Text editor (MicroDVD)
- VLC / players (both; VobSub needs its .idx)
- Subtitle Edit
macOS
- TextEdit (MicroDVD)
- VLC / IINA
Linux
- Text editor (MicroDVD)
- VLC / mpv
Web
- Convert to SRT or VTT first
Open a .sub file step by step
- Confirm the file really is a .sub. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with Text editor (MicroDVD) or VLC / players (both; VobSub needs its .idx).
- On Mac, use TextEdit (MicroDVD) or VLC / IINA.
- On Linux, try Text editor (MicroDVD) or VLC / mpv.
- Still stuck? Convert the .sub to SRT, which opens more widely.
Why can't I open my .sub file?
Almost always because no installed app understands SUB. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .sub at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .sub file
You can convert a .sub file to SRT, VTT using a conversion tool or the export menu of an app that opens it.
SUB has no fixed magic number, so there is no signature table on this page. Its bytes alone do not prove the format: identification relies on the extension, the structure of the content and the program that created it. The magic-numbers reference lists the formats that do carry one.
Frequently asked questions
What is a .sub file?
A .sub file holds subtitles, but in two different forms. It is either a plain-text MicroDVD file that times lines by video frame, or a binary VobSub picture stream that always comes with a matching .idx file. What opens it depends on which kind you have.
How do I open a .sub subtitle file?
Play it alongside the video in VLC. If it is the VobSub kind, keep the matching .idx file in the same folder, since the two work as a pair. If it is MicroDVD text, you can also open and edit it in any text editor.
Why is my .sub file unreadable, or why does it need an .idx?
Because it is the VobSub type, which stores subtitles as images rather than text, so it looks like binary in an editor and relies on a companion .idx file to index it. Keep the .sub and .idx together and load them in a player like VLC.
Related formats
Sources
Details on this page were checked against authoritative references. How sources are ranked and what is deliberately left out is set out in the methodology.