Block 4. The Artifact Gallery

A field guide to video compression artifacts — blocking, banding, ringing, mosquito noise, judder — what causes each and which metric catches it.

Macroblocking is the DCT block grid showing through your video. See what causes it, how the deblocking filter fights it, and how to measure it.

Video banding is the staircase in smooth skies and gradients. See what causes it, why metrics like VMAF miss it, and how to detect and fix it.

Mosquito noise and ringing are the shimmer and halos around sharp edges and text. Why they form, where they hurt, and how codecs and metrics handle them.

Video blur is lost high-frequency detail from compression or downscaling. Why it happens, telling it from intentional softness, and how metrics react.

Judder is uneven motion from frame-rate conversion like 3:2 pulldown; stutter is dropped frames. Why per-frame metrics miss them and how to catch them.

Color bleeding, color shift, and chroma subsampling smear saturated edges and text. Why luma-only metrics like VMAF miss them, and how to measure color.

Streaming video artifacts — switching, freezing, and tiling — come from the network, not the encoder, so picture metrics miss them. How to measure them.

Diagnose a video artifact in three tests: pause it, locate it, then bisect the pipeline to the stage — encoder, network, or display — that caused it.