melt \
clip1.dv out=74 \
-track \
-blank 49 clip2.mpeg \
-transition composite:"0=57%/10%:33%x33%; -1=0%/0%:100%x100%" progressive=1 distort=true in=50 out=74 a_track=0 b_track=1 sliced_composite=1 \
-transition mix:-1 in=50 out=74 a_track=0 b_track=1 \
$*
