Now we can use gstreamer to convert mjpeg stream from /dev/video0 into hyperion compatible stream on /dev/video1.
I am using this command (needs gstreamer, gst-plugins-good and gstramer-plugins-bad packages):
# /usr/bin/gst-launch-1.0 v4l2src device=/dev/video0 io-mode=2 ! image/jpeg, width=640, height=480, framerate=15/1 ! jpegparse ! jpegdec ! videoconvert ! video/x-raw, format=UYVY ! v4l2sink device=/dev/video1
this really helps, tu