Add a URL parameter named "url". The value of the param "url" would be a url to a video (mp4, avif, all of the supported video formats, and possibly a YT URL if GUI support comes out for it). Whatever that URL is in the url param (url/percent encoded or not), it will request it, treat it as a video, and attempt to extract it's frames. Other URL parameters can be added to it like "frames" and "frame-distance" or something like that to define those too.

Edit: Never mind about the URL param for YouTube, I forgot about the TOS.