From still pictures to an animation
Every picture you add becomes one frame. Drag the rows or use the arrows to change the order, or press Sort by name when the files are numbered, like screenshots or exported frames. The preview under the list plays the animation with the real timing, size and background, so you see the result before anything is encoded.
Pictures do not need to have the same size. Fit places each one in the middle and fills the rest with your background color, or leaves it transparent in GIF and WebP. Fill crops each picture from the center so the whole frame is covered. The output size follows the first picture, the largest one or a width you type; the height comes from the aspect ratio.
Speed and timing
Set the duration of every frame in milliseconds, for example 500 for two frames per second, or switch to frames per second. Turn on a different duration per frame to hold a title card longer or make the last frame stay before the loop starts again.
Browsers play GIF frames shorter than 20 milliseconds much slower than intended, so the shortest duration here is 20 milliseconds (50 frames per second). GIF stores durations in hundredths of a second; WebP and MP4 keep them to the millisecond.
GIF, WebP or MP4
GIF works everywhere, including email and old chat apps, but every frame is limited to 256 colors, so photos lose some smoothness and large GIFs get heavy. For that reason GIF output is limited to 1920 pixels on the longer side. Animated WebP keeps full color and soft transparency and is usually much smaller; all current browsers show it. MP4 is the smallest by far and fits social media posts, but it has no transparency and players decide themselves whether to loop, so a set repeat count is written into the video.