Convert SRT to SUB

A shrinking and specific group: owners of hardware from the DivX era and the years just after it. Standalone disc players that read video off a USB stick, car and headrest screens, some set-top boxes, and a scattering of cheap televisions that were built to one subtitle format and never updated. For those devices the format is not a preference, it is the only thing that appears on screen.

Everybody else should stop here. MicroDVD dates from 1998, is documented rather than standardised, and is treated as legacy across the board — the registry marks its support as patchy for exactly this reason. Nothing modern writes it, and modern subtitle editors read it in order to save something else.

A SubRip cue says when it appears: one minute, thirty-two seconds and 500 milliseconds. A MicroDVD entry says which frame it appears on, written as two numbers in curly braces followed by the text. The conversion multiplies each time by the frame rate and rounds to the nearest whole frame.

That difference is the whole subject of this page. A timestamp means the same thing against any copy of the video with the same running length, whatever it was encoded at. A frame number means a moment in time only if you know how many frames there are per second, and the file has no reliable way to tell anyone.

This page offers no way to set the rate. The site does ask for one where MicroDVD is the source rather than the destination, because reading such a file is impossible without knowing it; writing one in this direction uses the fallback, which is 25.

Say what that means rather than hiding it: if your video runs at 25 frames per second the output is frame-accurate, and if it does not, the subtitles are wrong in a way that grows as the film plays. Twenty-five is the right default because it is the European broadcast rate the format grew up alongside, and because a wrong guess is at least a consistent one that a player can correct in a single setting.

It drifts, steadily, and invisibly at first. A player reaching frame 250 at 23.976 frames per second gets there at 10.4 seconds rather than the 10.0 the file intended — four tenths of a second late, which nobody notices. The same 4.3 per cent over a ninety-minute film is close to four minutes of accumulated error, which is a subtitle for a scene that has not started yet.

The diagnostic is quick and worth memorising, because it separates two faults with different fixes. Check the first subtitle and one near the end. Wrong by the same amount at both ends is an offset, and any player can shift a file. Wrong by a growing amount is a rate mismatch, and the answer is to tell the player the correct frame rate rather than to nudge the timing.

The frustrating property of a rate mismatch is that it hides during exactly the period when somebody is checking. Play the first two minutes and everything looks right, copy the stick to the other room, and the problem surfaces forty minutes in with nobody at a keyboard. Whatever else this page persuades you to do, check a subtitle near the end of the film before deciding the file is good — it is the only test that distinguishes the two faults, and it takes as long as skipping to a timestamp.

There is a long-standing convention for recording the rate inside a MicroDVD file: a first entry with frame numbers of one and one, whose text is the frame rate, which players read as a declaration rather than displaying. Many files in circulation have it and many do not, because it was never part of a specification.

The output here does not include one. That leaves the decision with the player, which almost always assumes the frame rate of the video it is playing — the right assumption when the video is 25 fps and the wrong one otherwise. If your player lets you declare the subtitle frame rate, that is the field to use, and it is a faster fix than reconverting.

MicroDVD puts one entry on one physical line, so it needs an in-band character for a forced break, and that character is the vertical bar. A two-line SubRip subtitle arrives as a single line with a pipe between the halves, and players split it back into two.

The edge case is real and easy to miss: if your subtitle text already contains a pipe — a table, a transliteration convention, a piece of dialogue quoting a command line — it becomes a line break on playback. The format has no escape for it. Searching the SRT for the character before converting takes a second and is the only defence.

Cue text is copied verbatim. MicroDVD has its own small set of inline control codes for italic, bold, colour and font, written in curly braces at the start of a line, and the converter does not translate anything into them.

So an angle-bracket italic tag that a SubRip player honoured by convention travels into the SUB unchanged, and a MicroDVD player will draw it as characters rather than as italics. If emphasis matters on the target device, add the MicroDVD code by hand or strip the tags. Given that the support for those codes was always inconsistent between players, stripping is usually the better answer.

The rule that has never changed: the subtitle file sits in the same folder as the video and shares its base name exactly. film.avi and film.sub. One character of difference and nothing appears, and older devices give no indication that they looked and failed.

Two further constraints belong to the hardware rather than to the format. Many players read subtitles only from the same partition or the same USB stick as the video, not from a second one. And a number of them will not read a file whose name contains characters outside the basic Latin set, which is worth remembering when the video is named after a film with an accent in the title.

The structural difference is easy to miss when you open the output and worth understanding before you edit it. SubRip separates its blocks with a blank line and numbers each one; MicroDVD does neither. Every entry occupies exactly one line, entries follow each other with no separator at all, and a file of nine hundred subtitles is nine hundred consecutive lines beginning with a pair of numbers in braces.

That makes hand-editing unusually safe. There is no numbering to renumber when you delete an entry, no blank line to accidentally remove, and no multi-line block to keep together — deleting a subtitle is deleting a line, and moving one is moving a line. It also makes the file harder to read, because nothing separates one caption from the next visually, and it is why any error you introduce tends to affect exactly one entry rather than everything after it. Compared with SubRip, where a missing blank line makes every subsequent subtitle vanish in a strict player, that is a real if accidental virtue.

SubRip is the more widely supported of the two by a wide margin, and it is the format hardware makers implemented when they implemented anything. If a device is showing no subtitles for an SRT, the format is rarely the cause: the filename not matching, the file being on a different partition, and the character encoding being misread account for most of it.

Work through those three before converting. If the device then genuinely reads MicroDVD and nothing else, this conversion is the right tool and the frame rate is the one thing to get right. Keep the SRT as the file you maintain, and treat the SUB as a copy made for one machine.