I have some video that I would like to convert to images of frames every 2 sec.
E.g. If the video is 7 seconds long at 15 fps I would like to get frames 1, 31, 61, 91.
The command:
ffmpeg -i foo.mp4 -r 0.5 -f image2 -vcodec mjpeg foo%d.jpg
appears to do what I want, but which frame does it get? 1, 31, 61, 91 or 30, 60, 90 or 13, 43, 73, 103?
The first image will be from the very first frame.
Note that you very well may get an image or two more that you expect. I believe this is because of rounding and/or that ffmpeg creates a final images. E.g.: Is your video really 7s long? Or is it 7.63s long?