SUB File Format (.sub)
A MicroDVD .sub file is a plain-text subtitle track where each line names a start frame and an end frame instead of a timecode, in the form {start}{end}Text, so the same file displays differently depending on the frame rate of the video it's played against.
SUB at a glance#
| Full name | MicroDVD Subtitle |
|---|---|
| File extension | .sub |
| Category | Subtitles |
| Developer | Tiamat Software |
| First released | 2000 |
| MIME types | text/x-microdvd |
| Compression | Uncompressed |
| FileFlip support | FileFlip reads this format but does not write it |
What a .sub file can hold#
These are the things a SUB file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.
| Selectable text | Yes |
|---|---|
| Human readable | Yes |
Strengths and limitations of SUB#
What SUB does well
- Extremely compact, plain-text format that was trivial for early 2000s tools to generate alongside a fixed-frame-rate video rip
- Frame-accurate against the exact video it was authored for, since it references frame numbers directly
Where SUB falls short
- Frame-based timing means the file only stays in sync with the frame rate it was created for
- The .sub extension is also used by the unrelated, bitmap-based VobSub format, so a .sub file's contents can't be assumed from its extension alone
- Carries little to no styling and is not readable as a timeline without knowing the source video's frame rate
Recognize MicroDVD by its {start-frame}{end-frame}Text lines; it only makes sense alongside the exact video and frame rate it was timed against.
Convert MicroDVD to a time-based format like SRT as soon as the video might be re-encoded, retimed or played at a different frame rate, since that's what breaks its sync.
How to open a .sub file#
A .sub file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts SUB into a format your machine already opens, and it does it in the browser tab rather than on a server.
| Platform | Programs that open it |
|---|---|
| Windows | VirtualDub, Subtitle Edit, VLC |
| macOS | VLC |
| Linux | VLC, mpv |
| Web | FileFlip |
SUB questions people ask#
Why does a .sub file mean two different things?
The .sub extension is shared by two unrelated formats: MicroDVD, a plain-text subtitle file timed by frame number, and VobSub, a bitmap subtitle format that always comes paired with an .idx index file and stores images of each caption rather than text. Check whether your .sub has a matching .idx file next to it; if it does, it's VobSub, not MicroDVD.
Why do my MicroDVD subtitles drift out of sync?
MicroDVD times every line by frame number rather than by clock time, so the file only stays in sync with the exact frame rate it was authored for. Re-encoding the video at a different frame rate, or opening the file against a different cut, shifts every line further out of sync the longer the video runs.
Can I convert a MicroDVD .sub file to another format?
A MicroDVD .sub file can be read and converted into a time-based format like SRT, which removes the frame-rate dependency entirely. It cannot be produced as an output here, since writing frame-accurate MicroDVD subtitles requires knowing the exact frame rate of a specific target video.
Converting SUB files#
Convert SUB to another format
FileFlip does not write .sub files, so nothing on the site converts into this format. It works as a source only.
Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.