Extract jpeg files from mjpeg video on Linux

Just in case I ever need it again:

Extracting all frames from an mjpeg video as jpegs is easy and very fast with ffmpeg, because it does not need to decode and encode the pictures, just prepend the DHT to each one:

ffmpeg -i inputmpeg.avi -c:v copy -bsf:v mjpeg2jpeg frame_%d.jpg

Source ffmpeg documentation.