I'm a bit late at the party, but 4 years later, leancode made an image transformer for transforming assets images to webp. Search on pub. I looked briefly at the source code, it seems the github action is copying the cwebp executable. They communicated with it via dart:ffi. Maybe this can be leveraged in order to create an on demand conversion to webp, not just on your assets. https://github.com/leancodepl/flutter_webp