To convert a quicktime or any other format ffmpeg reads to jpeg use this command:

ffmpeg -i input.mov -qscale:v 1 -qmin 1 -qmax 1 output_%07d.jpg

1 is maximum quality 31 is lowest. The qmin and qmax lock the quality and gives a more consistent encoding level for sequences.

You can change the speed of your video using setpts video filter. The "old way" of creating timelapse or still frame was to first split up a video into individual frames, (for instance, as jpg's) then delete some and recombine the frames. Using the setpts filter is the new way and is faster and possibly less lossy :)

 needs editing