https://web.archive.org/web/20210621172103/https://trac.ffmpeg.org/wiki/Create%20a%20thumbnail%20image%20every%20X%20seconds%20of%20the%20video

Output one image every second, named out1.png, out2.png, out3.png, etc.
ffmpeg -i input.flv -vf fps=30 out%d.png

30 frames per second
ffmpeg -i input.flv -vf fps=30 out%d.png

Extract portions
ffmpeg -i champlin-vs-blain137.mp4 -ss 00:30:00 -to 00:30:15 -c copy c-vs-b-part1.mp4