Mosquito noise is ringing in motion - a shimmering swarm of small specks that flickers and crawls around a moving high-contrast edge, changing every frame like mosquitoes hovering around a lamp. The mechanism is the same Gibbs-phenomenon ripple, but because the codec re-solves a moving edge from scratch each frame - a different sub-pixel position, a different fall across the block grid, a different motion-compensated prediction - the overshoot-and-ripple pattern lands in a slightly different place each time, and the eye integrates the jitter as a crawling cloud. It is worst on high-contrast edges over calm backgrounds: scrolling subtitles, an animated logo, line art and screen content. The defining catch is that mosquito noise is temporal, so any measurement that scores one frame in isolation is structurally blind to it; per-frame PSNR, SSIM, and VMAF miss the flicker, and mean-pooling buries it further. Catch it with low-percentile temporal pooling, a no-reference edge-busyness detector, or by watching the clip move.
