How Live Photos work
A Live Photo is two files Apple keeps paired: a still image and a roughly 3-second video, linked by matching identifiers in their metadata. The Photos app only creates that link itself when the camera captures them, or when an app writes them to your library through Apple’s Photos framework — a web page can’t do that step.
So this tool does everything else: it builds the MOV in the right codec and container, loops the GIF to a natural length, and exports the key photo you pick. On your iPhone, open both files in a video-to-Live-Photo app from the App Store (intoLive is a well-known example), which saves them as a real Live Photo you can set as a Live wallpaper.
Tips for a great Live wallpaper
iPhone screens are tall, so portrait GIFs work best. Crop to a 9:16 ratio first and keep the subject centred. Seamless loops look most natural — a boomerang makes almost any clip loop smoothly. For a plain video instead, use GIF to MOV or GIF to MP4.