Why are my subtitles out of sync with the video?

Because the subtitle timings were worked out against a different copy of the same title. Cinema, Blu-ray and TV releases start at different moments, carry advert breaks, or run at a different frame rate.

How do you sync a subtitle with a video?

If the offset is constant, shifting every timestamp by the same amount is enough. QuickSubs works that amount out on its own by comparing the subtitle with the tracks embedded in the video, or by analysing where speech actually occurs in the audio.

What if the drift grows as the film goes on?

That comes from a frame-rate difference and shifting will not fix it: the timescale has to be rescaled. It is usually quicker to find a subtitle made for your exact copy of the video.

Out-of-sync subtitles: why it happens and how to fix it on a Mac

You found the right subtitle, but it runs half a second early. Or three seconds late. The film becomes uncomfortable to watch and you give up. Here is why it happens and how it gets fixed.

Why a subtitle does not match your video

An .srt file is just a list of lines with the time each one appears. It knows nothing about the video: if those times were worked out against a different copy from yours, they will not line up.

The three usual causes:

A different release of the same title. The cinema cut, the Blu-ray and the streaming version start at different moments. Some carry distributor logos before the first frame, others do not.
Advert breaks. TV captures have gaps where the adverts were. A subtitle timed against a clean copy drifts at every break.
A different frame rate. The classic case: film at 24 fps converted to European television at 25. The whole film runs about 4% faster, so the gap grows as it goes.

The two kinds of drift, which are not fixed the same way

Constant offset. The subtitle is always the same number of seconds early or late, start to finish. By far the most common, and it is fixed by shifting every timestamp at once.

Growing drift. It matches at the start and is several seconds out half an hour later. That is the frame-rate case, and shifting will not fix it: the whole timescale has to be stretched or squeezed.

How QuickSubs handles it

QuickSubs fixes the constant offset, which is what you will hit almost every time, and it does it by itself: drop the video with its subtitle and press sync. Under the hood it uses two methods and picks the best one available:

Against the subtitles already inside the video. Many .mkv files carry embedded subtitles in other languages. Comparing their timings with your .srt pins the offset down to the millisecond.
By listening to the audio. If the video has none, QuickSubs works out where people actually speak and compares that with where the subtitle claims they do.

You can also adjust it by hand if you would rather fine-tune it yourself.

What it does not do yet

Growing drift is not corrected automatically. If your subtitle starts fine and slides out of place, QuickSubs will fix the beginning and it will drift again later. In that case it is usually quicker to look for a subtitle made for your exact copy — the file-fingerprint search QuickSubs runs first is there for precisely that.

We would rather tell you up front.

While you are here

QuickSubs does not only sync: it finds and downloads the subtitle if you do not have one, and it can watch your download folders so the subtitle is simply there without you doing anything. No accounts to create, no API keys to paste.

See what QuickSubs does