WebP is a still image format, described in RFC 6386.
The “Making Software - Image Compression” book chapter also has a good overview of a number of image formats, including WebP.
There are two WebP variants: lossy (based on VP8) and lossless. Wuffs' VP8 implementation is in a separate package, as the WebM moving image format also uses VP8. There's no Wuffs WebM package yet but there might be in the future.