-i /opt/Torrent/3D/3Drender/pre.mkv -i out3.mp4 -lavfi "[0:v]scale=640:480,setsar=1:1[v1]; [1:v]scale=640:480,setsar=1:1[v2]; [v1][0:a:0][v2][1:a:0]concat=n=2:v=2:a=2[outv][outa]"