Trim the story before encoding
A long MP4 rarely makes a useful GIF. Choose a brief interval with a clear beginning and ending, and decide whether the loop should feel continuous. A cut made mid-action can create a noticeable jump when the last frame returns to the first.
Review the source's frame rate and intended display size. Reducing dimensions can make a loop easier to share, while too few frames may make motion look jerky. Avoid using a GIF as a substitute for a full video when viewers need the entire scene or its soundtrack.