How to slow down a narrator without breaking the lip sync
Tell Vizard Agent to slow the delivery and to keep it looking natural. It slows the voice and, for anyone on camera, slows the picture with them rather than only the audio. Then it re-times the on-screen graphics to the new pace and checks the mouths frame by frame before delivering.
What do you type into Vizard Agent?
Say the constraint out loud rather than assuming it. Without it, the reasonable reading of "slow her down" is to stretch the audio track, which works for a voiceover and looks wrong at once on anyone whose face is on screen while they speak. "A little slower" is enough of a brief for Vizard Agent to start from.
Prompt
What does Vizard Agent actually do?
Slowing a voice moves every word later, which pulls the mouth out of step, drags the graphics out of position and lengthens the cut. A voiceover can be slowed on its own because no mouth contradicts it. A presenter cannot: the picture has to slow by exactly the same factor. In the session behind this article it:
- Slowed the narration of an insurance ad that had come back too fast for the client to approve, and re-timed the whole cut around it.
- Slowed the on-camera presenters together with their picture, fixed the frame-exact lengths and rebuilt the timeline.
- Inspected the presenters' faces for stretching artifacts and verified the lip sync on the slowed presenters specifically.
- Measured the graphic and word timings against each other, re-timed the on-screen list to the new spoken line, and verified on real frames that it matched the words.
- Smoothed a shot with optical flow where the slow-down showed, and checked the interpolated frames for artifacts.
- Re-measured the levels and confirmed the closing mix.
When does this not work well?
There is a limit to how far speech can be slowed before it stops sounding like a person talking. Past roughly a tenth the ear starts to notice, and past a fifth it is obvious however good the processing is. A fixed runtime also fights it, since slower means longer, and fast motion behind the presenter makes interpolation struggle.
Common questions
What if the runtime is fixed? Then something has to be cut. Vizard Agent will tell you what it recommends.
Can it slow only one speaker? Yes. Name them and Vizard Agent leaves the others alone.
Will the captions still match? Yes. Vizard Agent re-derives them from the slowed cut.