Offset or drift?
Check the sync at the start of the video and again near the end.
- Same gap at both points: a constant offset. Shift the audio or subtitles by that amount.
- Gap grows (or shrinks) over time: drift. The timing runs at a slightly different speed, usually because of a frame rate mismatch or a variable frame rate recording.
To measure an offset, find a sharp sound such as a clap, a door or a hard consonant like p or t. Step frame by frame to where the visible action happens and compare it with when you hear it.
Fixing an audio offset
If lips move before you hear the words, the audio is late: shift it earlier (a negative value). If you hear words before the lips move, the audio is early: delay it (a positive value). Offsets of 40 to 100 milliseconds are already noticeable on faces; Bluetooth headphones can add their own delay, so check on speakers too.
Fix Audio DelayShift the sound earlier or later in steps of 10 ms. The picture is copied without re-encoding.Fixing a subtitle offset
Subtitles downloaded for a different release of a film are often a few seconds off. Shift every cue by the same amount: positive to show them later, negative to show them earlier. Find a clear line of dialogue, note when it is spoken and when the subtitle appears, and use the difference.
Subtitle Sync FixerShift every line of an SRT, VTT or ASS file at once.Fixing drift
Subtitles that drift usually come from a version of the video with a different frame rate. A film at 23.976 fps and a broadcast copy at 25 fps differ in speed by about 4%, so the error builds up to around two and a half minutes over an hour. The fix is to rescale the timing by the ratio of the two frame rates.
| Subtitles made for | Video you have | Use |
|---|---|---|
| 23.976 fps | 25 fps | 23.976 to 25 |
| 25 fps | 23.976 fps | 25 to 23.976 |
| 24 fps | 25 fps | 24 to 25 |
| 29.97 fps | 25 fps | 29.97 to 25 |
Audio drift in your own recordings often comes from variable frame rate (VFR). Phones and screen recorders vary the frame rate to save power, and some editors mishandle it. Converting the video to a constant frame rate before editing usually prevents it.
Change Frame RateConvert a variable frame rate recording to a constant 30 or 25 fps before editing.Video InfoCheck the frame rate of a file to see which conversion you need.Questions
Which way should I shift the audio?
If the voice comes after the lips move, the audio is late, so use a negative value to bring it earlier. If the voice comes first, use a positive value to delay it.
Why are my subtitles fine at the start but wrong at the end?
That is drift, usually from a frame rate difference between the video the subtitles were made for and yours. Use a frame rate fix instead of a fixed shift.
Does shifting audio reduce picture quality?
No. The video stream is copied untouched, so the picture is exactly the same as before. Only the timing of the sound changes.
Could my headphones be the problem?
Yes. Bluetooth headphones add their own delay. Check the video on wired headphones or speakers before changing the file.