color=c=black:size=854x480 [background];
[0:v] scale=-2:480:flags=fast_bilinear, crop=w=iw*0.5:h=ih*1.0:x=iw*0.25:y=ih*0.0 [video0];
[1:v] scale=-2:480:flags=fast_bilinear, crop=w=iw*0.5:h=ih*1.0:x=iw*0.25:y=ih*0.0 [video1];
[background][video0] overlay=eof_action=pass [combined0];
[combined0][video1] overlay=main_w*0.5:main_h*0.0:eof_action=pass [combinedAll];
[combinedAll] fps=30;
anullsrc [abackground];
[abackground][0:a][1:a] amix=inputs=3,volume=1.0