I have found the command
ffmpeg -i rtsp://10.2.69.201:554/ch0_0.h264 -f image2 -vf fps=fps=1/120 img%03d.jpg
but it fail if I'm not on network. I tryed on my on computer but I have bind error. I would like to have a command like or a mix of these one:
ffmpeg -f v4l2 -s 640x480 -i /dev/video0 output.mpg
Thanks for your help. This is appreciated if that possible