You can grab sample webp images to use here there:
package libwebp; function DecodeWebp(webpByteArray:ByteArray):BitmapData; function EncodeWebp(input:BitmapData, quality:Number):ByteArray;
It is compiled with 0.3.1 and supports lossy, lossless compression and alpha channel. No animations yet.
Due to flash's dynamic recompilation, the first time you decode a webp image will take a bit longer than usually, but on later calls it will be faster.
Webp for ActionScript3 come in two flavors:
You can run the SWC version in any webpage and AIR application, but it will run ~2x-5x slower than using an ANE.
Also there is a ANE that could be used on AIR for Windows and Android at this moment. iOS, linux and Mac ANEs will be available in a future version. For those platforms you can use the SWC version.