An animated sticker looks like a tiny video, but under the hood it's closer to a flipbook. Here's what's actually going on.
It's just a stack of still images
Every animated format, GIF, WebP, or otherwise, stores a series of individual frames, each one a complete still image. Played back fast enough, usually somewhere between 10 and 30 frames per second, your eye reads the sequence as smooth motion instead of a slideshow.
Color count is where formats really differ
Classic GIF is limited to 256 colors per frame, a restriction from 1987 that's never gone away. That's fine for simple line art and flat colors, but it's why gradients and skin tones in GIFs sometimes look slightly banded. WebP has no such limit, which is part of why TikTok's stickers look cleaner in their original format than they do after converting to GIF.
Compression works frame by frame, and between frames
Formats get smaller by not fully redrawing pixels that didn't change from one frame to the next. A sticker where only a character's mouth moves can store most of the image once and just update the small region that's animating. This is also part of why some conversions produce oddly large files. Converting to a format with worse inter-frame compression means the file has to store more redundant information to look the same.
The loop is just a setting, not a special trick
Looping doesn't require anything clever. Both GIF and WebP have a simple flag in the file telling whatever's playing it to go back to frame one once it hits the end, either a set number of times or forever. That one setting is the entire difference between an animation that plays once and one that loops indefinitely.