Datamosh

The compression falls apart and the picture smears its own movement across the frames that follow. Colour blocks drag, faces dissolve into the direction they were travelling.

It looks like a recording failing rather than an effect being applied. That register of breakage is the reason it gets used for grief, for memory, and for anything coming apart.

Video compression stores occasional full frames and, between them, only the movement from the frame before. Remove the full frames and the movement data keeps being applied to the wrong picture, which is the smear.

It needs motion to work with, as the note says. The artefact is made of movement vectors, so a static shot has nothing to drag and the effect does almost nothing.

Large simple movements smear most cleanly. A hand sweeping across frame or a camera whip pulls broad bands of colour. Fine detailed motion turns into noise instead.

Use it on a transition between two shots, on a memory going, and in music pieces where the image should feel like a file rather than a photograph.

Skip it when anything has to stay legible. The effect destroys detail by design.

A stutter repeats or drops whole frames, so the picture stays sharp and the timing breaks. Datamosh keeps the timing and breaks the picture, so the image stays continuous while the detail liquefies.

The test is sharpness. Clean frames arriving in the wrong order is a stutter. Smeared frames arriving on time is datamosh.

A clean shot comes back with a light glitch overlay on it. Say the compression is breaking down and the blocks are bleeding into the movement, then name the movement that is doing the smearing.

The second failure is a static subject with artefacts painted over it. Give the shot a large motion, a camera whip or a body crossing frame, so the effect has something to drag.