Banding is the appearance of discrete steps across a region that should be a continuous gradient — a sky, a studio backdrop, a fade to black, a soft vignette.
It is worth separating from other artifacts because its usual cause is different. Blocking comes from too few bits. Banding comes from too few values: 8-bit video has 256 levels per channel, and a gentle gradient spread across a wide area may need more distinct levels than that to look smooth. Compression makes it worse by quantising away the dither noise that was hiding the steps, but the steps were latent in the format.
Which is why the instinctive fix often fails. Doubling the bitrate on a banded sky may barely change it, because the encoder is already reproducing the limited set of values it was given faithfully.
What actually helps:
- Encode in 10-bit where the pipeline supports it. More levels, and it helps even when the source is 8-bit and the output will be viewed as 8-bit, because intermediate calculations stop rounding into the same steps.
- Add a little grain or dither before encoding. Breaking up the boundaries costs bitrate and looks better than clean steps.
- Avoid unnecessary colour-space conversions, each of which is another rounding opportunity.
Animation and screen content suffer most, because they contain large areas of synthetic gradient with no natural noise to mask the transitions. Camera footage usually carries enough sensor noise to hide them.