How to stop separately rendered segments drifting out of sync when you join them
Ask Vizard Agent to check each segment's frame count against the count it was supposed to have. Segments rendered one at a time land a frame or two long, the errors add up along the joins, and by the end the voice sits behind the picture. Vizard Agent rebuilds the render so every segment hits an exact count, then verifies continuity before the audio returns.
What do you type into Vizard Agent?
Describe the symptom rather than diagnosing it yourself. Sync that is fine early and clearly wrong late is a specific shape of problem, and saying so points Vizard Agent straight at accumulated rounding rather than sending it hunting for one bad clip in the middle. Ask for frame counts, not seconds, because seconds hide the error.
Prompt
What does Vizard Agent actually do?
The fix isn't a nudge at the end. It's making every segment come out at the length it was asked for, because if the renderer keeps producing approximately-right segments, every future change brings the same drift back. Durations in seconds round away the evidence, so the check counts frames. In the session behind this article it:
- Concatenated the picture of a documentary assembled from a few dozen separately rendered segments, and separated the voice track.
- Checked each segment's frame count against its intended count and found the drift was per-segment rounding, not one bad clip.
- Rewrote the renderer to produce exact frame counts, re-rendered every segment and verified the counts before joining anything.
- Concatenated again, checked continuity across the joins, and confirmed the last spoken word against the source length so a short tail couldn't clip it.
- Put the voice track back and re-measured.
When does this not work well?
Not every late sync problem is accumulation, and Vizard Agent will tell you when it isn't. A mismatched frame rate, variable frame rate footage from a phone, or an audio track stretched somewhere upstream will all produce very similar symptoms from a completely different cause. Sync that's wrong from frame one is an offset, not drift.
Common questions
Why frames and not seconds? Seconds round. Vizard Agent counts frames because that is where the error lives.
Does the audio need re-cutting? No. Vizard Agent puts the same voice track back onto a correct picture.
Will it catch a single bad clip too? Yes, and Vizard Agent will say it is a jump rather than drift.