-i /path/to/sequence/%d.png - path to image sequence where each image is name 1.png to n.png. Note there are no leading zeros in file names. For 0-padded file names, the pattern is %0nd where n is the number of digits.
-vcodec libwebp - set the video codec to generate WebP images
-pix_fmt yuv420p - set the pixel format (color space). YUV420 is the only supported one for lossy and RGB is the only supported one for lossless.
-loop 0 - loop the animated WebP
-s 720:720 - resize the output
-quality 50 - set the quality value. 75 is the default and lower values will yield lower quality but smaller files. It may make more sense to use the preset flag instead for some use cases. See the ffmpeg-codec page for more information, listed at the top of this document.