Get the list of I-Frames in a video in FFMPEG / Python

Question

I'm trying to select say 10 frames from a given video, possibly with highest variety and scenes. I would like to experiment with various selection scenarios, but the good thing is that the notion of I-frame inherently means scene changes! So I would like to get the I-frames. But maybe there are many I-frames, so probably I have to sample them.

How can I get the list of all I-frames's frame_number in a video in FFMpeg or Python? I would like to use the list to select only 10 of them and save them as PNG/JPEG.

Solution 1

Getting insights from here, I was able to do it with ffprobe:

def iframes():
    if not os.path.exists(iframe_path):
        os.mkdir(iframe_path)
    command = 'ffprobe -v error -show_entries frame=pict_type -of default=noprint_wrappers=1'.split()
    out = subprocess.check_output(command + [filename]).decode()
    f_types = out.replace('pict_type=','').split()
    frame_types = zip(range(len(f_types)), f_types)
    i_frames = [x[0] for x in frame_types if x[1]=='I']
    if i_frames:
        cap = cv2.VideoCapture(filename)
        for frame_no in i_frames:
            cap.set(cv2.CAP_PROP_POS_FRAMES, frame_no)
            ret, frame = cap.read()
            outname = iframe_path+'i_frame_'+str(frame_no)+'.jpg'
            cv2.imwrite(outname, frame)
        cap.release()
        print("I-Frame selection Done!!")


if __name__ == '__main__':
    iframes()

Solution 2

This seems like an X/Y problem, so I'll propose several different commands:

List of timestamps

If you want to output a list of timestamps for each keyframe:

ffprobe -v error -skip_frame nokey -show_entries frame=pkt_pts_time -select_streams v -of csv=p=0 input
0.000000
2.502000
3.795000
6.131000
10.344000
12.554000

Note the -skip_frame nokey.

select filter

Another method is to use the select filter with the scene option to output your thumbnails:

ffmpeg -i input -vf "select=gt'(scene,0.4)',scale=160:-1" -vsync vfr %04d.png

Solution 3

This will output all the i frames as PNG images.

ffmpeg -i 2.flv -vf "select=eq(pict_type\,I)" -vsync vfr frame-%02d.png

Credit to this comment a similar superuser.com question. How to extract all key frames from a video clip?

Hope that helps. Cheers.

Ian

Comments

[Tina J]

Thanks, but I know this. What I asked is the array of the I-frame indexes in code!