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Choose how much earlier, preview the timing, then export.
When the picture leads and the sound lags — you see a mouth move before you hear the word — the soundtrack needs to start earlier. This tool trims a precise amount off the head of the audio, in milliseconds or in source frames, and previews the corrected timing so you can confirm the fix before writing the file.
Advancing means cutting from the start of the soundtrack, so whatever occupied that time is gone. For the tens of milliseconds involved in a typical sync fix, that is inaudible — it is a fraction of a syllable of room tone. It only matters if you advance by a large amount and the audio begins with something you need, such as a clap, a first word or the downbeat of a track. If that is a risk, check the start of the exported clip specifically.
Audio arriving late is the direction viewers notice fastest, so it is worth being precise. Work in 20 ms steps and judge on a continuous sentence rather than a single word: one word can appear correct by chance while the rest of the sentence is clearly off. If you are matching an editing timeline, frames are easier to reason about — two frames at 30 fps is about 67 ms. If you are unsure which direction the error runs, the sync tool lets you slide the audio both ways and settle it by ear.
When the picture leads the sound — a mouth moves before the word arrives. Trimming the head of the audio pulls the soundtrack earlier and closes the gap.
Technically yes: the trimmed amount is removed from the start. At typical sync amounts that is a fraction of a syllable of room tone, but check the opening if you advance by a large amount.
Milliseconds when working from device latency or by ear, frames when matching an editing timeline. One frame is roughly 33 ms at 30 fps and 17 ms at 60 fps.
Errors under about 20 ms are inaudible to most people. Between 40 and 50 ms viewers start to notice, so that is the range worth correcting.
Use the delay tool, which adds silence at the head to push the soundtrack later — the opposite correction.
