SUB File — What It Is and What Opens It

What SUB is

SUB is a plain-text format you can open in any editor. It is used for subtitling.

The extension is .sub, and the full name is MicroDVD Subtitle. Both matter less than what the file can hold, which is what the rest of this page is about.

Where SUB came from

It dates from 1998.

A format that has been readable for that long is a format worth trusting with something you want back in ten years.

The specification is published, but by its owner

It is written down and implementable, though the vendor decides what the next version looks like. In practice that is enough for the file to keep opening; it is not enough to be sure of it.

It is a legacy format

It still opens everywhere and is still written by older tools, but nothing new is being built around it. Convert what you mean to keep, and do not choose it for something starting today.

What opens SUB

VLC and Subtitle Edit read it, and so do most programs of the same kind.

If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.

Opening it in a browser

No browser reads it.

That is the single most common reason to convert it: not that the format is bad, but that the place you want to show the file cannot read it.

It is a working format

SUB is meant to be opened and changed. Keep the file in this format for as long as the work is going on, and export from it whenever a finished copy is needed.

What goes wrong with it

The recurring complaints: support outside its home ground is uneven.

None of these is a reason to avoid the format. They are the things worth knowing before you are surprised by one, which is a different claim and a more useful one.

The facts, in one place

Identifiers and provenance for the SUB format.
Extension	.sub
Media type	text/plain
First published	1998

What is a SUB file?