AVS shipped inside Winamp as a construction kit: stackable effects, per-frame and per-pixel expressions, audio data exposed to user code, presets shareable as tiny files. A worldwide community traded thousands of them, one-upping each other in what a media player could render in 2001.
The framework was open-sourced in 2005, and its alumni and aesthetics flowed into MilkDrop, shader culture, and VJ software.
AVS mattered as infrastructure: it put programmable audio-reactive graphics on tens of millions of ordinary PCs, making visualizer literacy a mass phenomenon rather than a specialist craft. Most people’s first mental image of music visuals was rendered by it or its successor.