How to fix audio that only goes out of sync partway through

Last updated 2026-09-04 · 7 min read

What is the short version?

Audio that is out of sync from the first frame is a simple offset. Audio that is fine for seven minutes and wrong afterwards is something else entirely — a place in the edit where the picture gained or lost time and the sound did not.

1. Go to Vizard Agent with the current version.
2. Say the timecode where it goes wrong.
3. Say that everything before it is fine.

What do you need before you start?

The rendered video and the timecode. "It goes out of sync around seven minutes five" is a genuinely valuable piece of information, because it tells Vizard Agent to look for a cause at that point rather than assuming a constant offset across the whole file.

• The current render. The one you watched.
• Where it starts. Roughly is fine.
• That it was fine before. The key detail.
• Which way it is off. Early or late, if you can tell.
• The source, if separate. For the comparison.

What do you type into Vizard Agent?

Give the timecode and the fact that it was correct up to that point. Without the second half, a reasonable reading is that the whole track needs shifting, which will fix the last three minutes and break the first seven.

Prompt

Variants worth knowing:

• "It's fine before that." Rules out a global offset.
• "Find why." Asks for the cause, not the patch.
• "Check the whole thing after." Drift can start twice.

What does Vizard Agent actually do?

Here is the order Vizard Agent worked in on a real eight-and-a-half-minute video whose sound drifted away from the picture in its final third. Steps five to seven are the whole diagnosis, and all three of them happen before Vizard Agent adjusts anything at all.

1. Renders the assembled cut with all the reframes and push-ins.
2. Verifies the base timeline frames and locates missing seconds.
3. Measures speech and music loudness to set the mix.
4. Has the finished edit watched through for sync and polish problems.
5. Compares the final frames against the source to locate the drift.
6. Runs the comparison again across a different span to confirm it.
7. Measures the exact video offset after the freeze section.
8. Rebuilds the assembly with the corrected sync.
9. Verifies the sync is fixed on the rebuilt file.
10. Reviews the rebuilt tail frames specifically.
11. Extracts dense frames across every fixed transition.
12. Reviews all the transitions frame by frame.

Step seven is the answer, and it names the culprit: a freeze section. Holding a frame is a picture-only operation, and if the audio underneath it is not held by exactly the same number of frames, everything after that point is offset — permanently, and by the same amount.

That is why step eleven matters. Once you know one structural feature caused it, every other one in the edit is a suspect, so the transitions are all checked rather than just the one that was reported.

What does the result look like?

A version where the picture and the sound agree all the way through, fixed by Vizard Agent at the exact point where they stopped agreeing rather than compensated for with a nudge applied evenly across the whole file.

The distinction is not academic. A global nudge that makes minute eight correct makes minute two wrong by the same amount, and the person who reported the problem will watch the beginning first.

When does this not work well?

Some drift is not in the edit at all — it is baked into the recording itself, and it grows continuously from the first frame rather than starting at one identifiable point. That is a different diagnosis with a different fix, and Vizard Agent will tell you which of the two you have.

• Variable frame rate recordings. Phones do this; the drift is gradual.
• Sample rate mismatches. A slow, constant creep from the first frame.
• Very small offsets. Below a frame or two, nothing is measurable.
• Several causes at once. Each has to be found separately.
• A source you no longer have. There is nothing to compare against.

How do you fix a result that came back wrong?

Say what you now see and where. Vizard Agent keeps the frame comparison, the measured offset and the assembly script from the first pass, so a second drift point gets found by the same method rather than by re-examining the entire file again from scratch.

• "It drifts again later." A second point located and measured.
• "Now the start is off." The correction was applied too broadly.
• "Only the music is late." That layer re-aligned on its own.
• "The transition looks odd now." Rebuilt and checked frame by frame.

How does Vizard Agent compare to doing it yourself?

By hand, the temptation is to grab the audio track and slide it until the bit you were watching looks right. That works, and it silently breaks everything before the drift point — which is why sync problems have a habit of coming back in the next round of notes.

Common questions

Do I need the exact timecode? No. Roughly where you noticed it is enough for Vizard Agent to start.

Why does it matter that it was fine before? Because that rules out a constant offset, which needs a completely different fix.

Can it just nudge the audio? It can, and Vizard Agent will tell you why that usually makes things worse.

What causes it most often? An operation that changes the picture's duration without changing the audio's. Vizard Agent names it.

Can it check the whole file? Yes. Ask Vizard Agent to verify every transition, not only the reported one.

What if my source is a phone recording? Then variable frame rate is likely. Vizard Agent will say if the drift is gradual.

Does the fix re-render everything? Vizard Agent rebuilds the assembly. Nothing is regenerated.

Will the captions still match? Yes. Vizard Agent re-derives them against the corrected timeline.

Can it fix drift in the source itself? Yes, by conforming the file first. Say so, because it changes the approach.

How small an offset can it find? Vizard Agent measures to a frame, which is roughly where the eye starts to notice.

Can it tell me the cause? Yes, and it is worth asking — it usually tells you what to avoid next time.

Does removing the music help? Only your ability to hear it. Vizard Agent measures rather than listening.

What if two things drift? Vizard Agent finds each one separately and reports both.

Why not just re-edit it? Because the edit is fine. One operation inside it moved the picture and not the sound, and that is a two-minute fix once you know which one.