Explanation:

• split: This duplicates the GIF stream.
• trim: Cuts the frames at specific points (start_frame=X and end_frame=N where X is the frame you want to start with, and N is the total number of frames).
• concat: Combines the two parts back together so the loop remains seamless.
• setpts=PTS-STARTPTS: Adjusts the presentation timestamps so the frames play sequentially.