How to make a 3d movie with ffmpeg

how to combine two seperate videos into one left-right 3d video

1. Convert both movies to png still images

1. ffmpeg -r 20 -i test01-left.avi -r 20 -s 640x480 frames-l/%09d.png

2. ffmpeg -r 20 -i test01-rigth.avi -r 20 -s 640x480 frames-r/%09d.png

2. Bash script for putting still images side by side, using imagemagick's montage command

 a=1 
 while [ $a -lt 2416 ]  
 do 
    b=`printf "%09d" $a` 
    montage frames-l/$b.png  frames-r/$b.png -geometry 320x240+0+0 frames/$b.jpg 
    let a++
 done

3. Convert images to avi

1. ffmpeg -i %03d.png -an -vcodec copy -f avi outputfile.avi