A GIF stores its animation as a series of full image frames stacked together, which is a simple approach but not a very efficient one. MP4 uses video compression instead, meaning it only stores what changes between frames rather than redrawing the whole picture each time. That difference is why the exact same animation can be ten or twenty times smaller as an MP4 than as a GIF, while still looking just as smooth, sometimes smoother since MP4 also supports more colors per frame than a standard GIF palette allows.
When you convert here, the tool reads through every frame of your GIF in order, along with its timing data, and rebuilds that sequence as a proper video stream. Choosing HD keeps the original resolution and frame timing as close to the source as possible, which is the better option if you plan to use the file somewhere quality matters, like a portfolio site or a presentation. SD quality reduces the bitrate slightly, which is useful if your priority is a smaller file for quick sharing rather than maximum sharpness.
This conversion is the reverse of what our GIF compressor does for animations you want to keep as a GIF. If your file is the other direction, meaning you have a video and want a looping GIF out of it instead, that is a different process entirely since you would be going from a continuous video stream back into discrete frames. And if the animation you are starting from is not even downloaded yet, our GIF downloader handles grabbing it from a link first.
One thing worth knowing before you convert: MP4 files do not autoplay and loop on every platform the way GIFs do by default. Some apps require a tap to start playback, and looping behavior depends on how the platform itself handles short video clips. If your GIF is meant to play automatically the instant someone sees it, like a reaction image in a chat thread, keeping it as a GIF or using our WebP to GIF converter for the lighter weight WebP format might suit that use case better than MP4 does.