I know this is quite late, but for anyone still looking for a WebP encoder in Go: I recently released nativewebp, a native WebP encoder written entirely in Go. Unlike most WebP encoders, this one has no dependencies on libwebp or other external libraries, making it perfect for Go projects that value simplicity and portability.

Currently, the encoder supports only WebP lossless images (VP8L). It’s about ~50% faster than Go's native PNG encoder, while producing ~25% smaller files!

You can find the package here: https://github.com/HugoSmits86/nativewebp