ffmpeg -i monitor.flv -re -vf "[in] pad=1576:960 [left]; movie=camera1.flv, scale=676:480 [right]; movie=camera1.flv, scale=676:480 [bottomright]; [left][right] overlay=870:0 [tmp]; [tmp][bottomright] overlay=870:480" -c:v libx264 -preset ultrafast mosaic.flv