Get the frame size:
export FRAME=720x576
ffmpeg \
-f lavfi -i color=size=${FRAME}:rate=25:color=black \
-f lavfi -i anullsrc=channel_layout=stereo:sample_rate=44100 \
-s ${FRAME} -pix_fmt yuv420p -r 25 \
-t 600 empty.dv
cat empty.dv > /dev/dv1394