Subtitle Timing Shifter

There are two different faults here and only one of them is a delay. Work out which you have before you touch anything: check the sync at the start of the film and again near the end. If the gap is the same at both, it is an offset. If it has grown, it is drift, and no amount of shifting will fix it.

The distinction matters because a player’s own subtitle delay setting only handles the first. Nudging it is a per-device fix that has to be repeated everywhere and lasts until the file is opened somewhere else; changing the timestamps is a resync of the file itself, and it travels with it.

A constant offset comes from a different cut — a distributor’s logo, a longer title sequence, an advert break edited out. Every cue is wrong by the same amount, so every cue moves by the same amount.

Drift is a frame-rate problem. Subtitles authored against a 25 fps broadcast master, played against a 23.976 fps film transfer, are right at the start and minutes out by the end. The two are not different by a constant but by a ratio, so every timestamp has to be multiplied rather than added to. 25 to 23.976 is the common pair, and it makes the subtitles run about four percent slower.

Negative times are clamped and counted, not hidden. If a shift pushes cues before the start of the file, that usually means the sign is the wrong way round — you asked for earlier when you wanted later. The status line says how many were clamped so the mistake surfaces here rather than in front of an audience.

The file is written back in the format it arrived in, with one exception: an .ass or .sbv file comes back as SubRip, because neither can be written from a start, an end and some text without inventing the rest of it. The status line says so when it happens. If you want a different format on purpose, convert it as a separate step.

Press Load a sample. Three cues: one at two seconds, one at ten minutes, one at an hour and a half.

Leave the mode on constantly early or late and the amount at -2.5. Every cue moves back two and a half seconds — the first to 00:00:00,000, and the status line reports one cue clamped at zero, because two seconds minus two and a half is below the start of the file.

Now switch to drifts further out, with 25 as the timing and 23.976 as the video. The first cue barely moves — from two seconds to about 2.085. The last one moves by more than three and a half minutes. That difference is the whole point: a fault that is invisible in the opening scene and unwatchable in the closing one.

Which is also the diagnostic. If your subtitles look fine for the first ten minutes and hopeless at the end, do not reach for the offset — no single number fixes it.