RE: LeoThread 2024-10-17 14:49

[ahmadmanga]

Conversation with ChatGPT4o:

Prompt: Can I use ffmpeg to rotate the frames of a gif images so I make it start in the middle of the loop while keeping the loop intact?

Summarized Response:

To shift the starting point of a looping GIF while keeping it seamless, you can reorder its frames using ffmpeg. An efficient method involves duplicating the GIF and trimming it to start at your desired frame:

ffmpeg -i input.gif -filter_complex "[0:v]split[original][copy];[copy]trim=start_frame=X:end_frame=N,setpts=PTS-STARTPTS[part1];[original]trim=start_frame=0:end_frame=X,setpts=PTS-STARTPTS[part2];[part1][part2]concat=n=2:v=1[out]" -map "[out]" output.gif

Replace X with your desired starting frame and N with the total number of frames.

To find the total number of frames in your GIF, use:

ffprobe -v error -count_frames -select_streams v:0 -show_entries stream=nb_read_frames -of csv=p=0 input.gif

Full Conversation in comments.

Comments

[ahmadmanga]

You want to take a looping GIF, rotate the sequence of its frames so that the animation starts from the middle, and ensure that the GIF still loops seamlessly as if it were unchanged. Essentially, you're asking how to shift the order of the frames, so the animation's starting point is different, without breaking the continuous loop.

Here's how you can achieve that with ffmpeg:

1. Extract the frames of the original GIF.
2. Reorder the frames so that the middle frame becomes the first, while keeping the loop continuous.
3. Rebuild the GIF with the newly ordered frames.

[ahmadmanga]

Here’s how to do it step by step:

1. Extract the frames of the GIF:

   ffmpeg -i input.gif frame_%04d.png
   

   This command will extract all frames and save them as separate PNG files (frame_0001.png, frame_0002.png, etc.).

2. Shift the frames:
   Let's say your GIF has 20 frames, and you want to start at frame 10. You would need to rename the frames so that the 10th frame becomes the first, followed by the rest of the frames, and then looping the first part back.

   You can use a simple script (e.g., in Python) to rename the files, or manually if it's a small set of frames. For example:

   • Rename frame_0010.png to frame_0001.png,
   • frame_0011.png to frame_0002.png,
   • and so on until you loop back to the earlier frames (frame_0001.png becomes the last).

[ahmadmanga]

Yes, there’s a more efficient way to shift the starting point of a looping GIF directly using ffmpeg without manually extracting, renaming, and reassembling the frames. You can use filters to rearrange the frames in the GIF directly.

Tools for an even simpler approach:

If you prefer a graphical tool, EZGIF.com is an online tool that allows you to rearrange GIF frames visually and quickly. You can upload the GIF, reorder the frames, and export it directly from the browser.

Let me know if you'd like help with a different approach!

[ahmadmanga]

Solution using ffmpeg:

You can use the select filter in ffmpeg to adjust the order of frames without needing to extract and rename them manually. Unfortunately, ffmpeg doesn't natively support "rotating" frames within a loop in one command, but a workaround can be to duplicate the frames and trim them, so the loop starts at a new point.

Here’s a more streamlined approach:

1. Duplicate the GIF (append the frames of the GIF to itself).
2. Trim the new starting point and cut the GIF down to its original length, ensuring that the loop is still seamless.

The command to do this would look like this:

ffmpeg -i input.gif -filter_complex "[0:v]split[original][copy];[copy]trim=start_frame=X:end_frame=N,setpts=PTS-STARTPTS[part1];[original]trim=start_frame=0:end_frame=X,setpts=PTS-STARTPTS[part2];[part1][part2]concat=n=2:v=1[out]" -map "[out]" output.gif

[ahmadmanga]

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.