MP4, WebM and WebP are not the same thing

WebP is an image format. WebM is a video container, usually VP8 or VP9 plus Opus. MP4 is a different container, usually H.264 plus AAC. They sit next to each other in menus and the names look alike.

If you asked for a video and received a still picture, the tool confused WebM with WebP — or it only implemented an image encoder. Batonbox labels WebM as “WebM video — not WebP” and writes a real video file.

GIF is the third trap: it is an animation, not a movie with a soundtrack. Use it for short loops. Use MP4 or WebM when you need audio or more than a few seconds.