Do I have to mask or roto anything?

No. The subject and the background are separated for you, and the melt is applied to one side of that split.

What footage does it need?

A clip with a clear subject in it, ideally a person, reasonably separated from the background. Shots with no obvious subject will simply melt everywhere.

Can I melt the person instead of the background?

Yes. Turn on "Mosh the subject" and the effect swaps sides.

Why is the whole frame melting?

No subject was found in the shot. The effect falls back to moshing everything rather than pretending it found someone.

Depth Mosh

Depth Mosh splits the frame in two and only lets one half fall apart. The background dissolves into smeared, melting compression rot while the person in front of it stays completely sharp, as if they were the only thing the codec still understood. It can be flipped, so the subject liquefies while the world behind them holds perfectly still.

How to use Depth Mosh

Upload a clip with a clear subject, ideally a person facing the camera.
Play it back. The background starts rotting immediately; the subject does not.
Raise Freeze Length to let the background melt further before it resets.
Flip "Mosh the subject" if you want the melt on the person instead.
Export as MP4 at source resolution.

Tips

Longer Freeze Length gives the background more time to visibly liquefy. Short values just look like a compression fault.
It needs a clear subject in frame, ideally a person, reasonably separated from what is behind them. On a shot with no obvious subject the whole frame melts.
Keep Edge Feather tight and the subject looks stamped onto a dissolving world. That contrast is the entire effect.
Flip "Mosh the subject" and you get the opposite: the person melts and the room stays still.

Frequently Asked Questions

Do I have to mask or roto anything?: No. The subject and the background are separated for you, and the melt is applied to one side of that split.
What footage does it need?: A clip with a clear subject in it, ideally a person, reasonably separated from the background. Shots with no obvious subject will simply melt everywhere.
Can I melt the person instead of the background?: Yes. Turn on "Mosh the subject" and the effect swaps sides.
Why is the whole frame melting?: No subject was found in the shot. The effect falls back to moshing everything rather than pretending it found someone.

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