ffmpeg -i 1,1.mp4 -i 1,2.mp4 -i 1,3.mp4 -i 1,4.mp4 -i 2,1.mp4 -i 2,2.mp4 -i 2,3.mp4 -i 2,4.mp4 -i 3,1.mp4 -i 3,2.mp4 -i 3,3.mp4 -i 3,4.mp4 -i 4,1.mp4 -i 4,2.mp4 -i 4,3.mp4 -i 4,4.mp4 -filter_complex "nullsrc=size=6832x3840 [base];[0:v] setpts=PTS-STARTPTS, scale=1708x960 [1,1];[1:v] setpts=PTS-STARTPTS, scale=1708x960 [1,2];[2:v] setpts=PTS-STARTPTS, scale=1708x960 [1,3];[3:v] setpts=PTS-STARTPTS, scale=1708x960 [1,4];[4:v] setpts=PTS-STARTPTS, scale=1708x960 [2,1];[5:v] setpts=PTS-STARTPTS, scale=1708x960 [2,2];[6:v] setpts=PTS-STARTPTS, scale=1708x960 [2,3];[7:v] setpts=PTS-STARTPTS, scale=1708x960 [2,4];[8:v] setpts=PTS-STARTPTS, scale=1708x960 [3,1];[9:v] setpts=PTS-STARTPTS, scale=1708x960 [3,2];[10:v] setpts=PTS-STARTPTS, scale=1708x960 [3,3];[11:v] setpts=PTS-STARTPTS, scale=1708x960 [3,4];[12:v] setpts=PTS-STARTPTS, scale=1708x960 [4,1];[13:v] setpts=PTS-STARTPTS, scale=1708x960 [4,2];[14:v] setpts=PTS-STARTPTS, scale=1708x960 [4,3];[15:v] setpts=PTS-STARTPTS, scale=1708x960 [4,4];[base][1,1] overlay=shortest=1:x=0:y=0 [tmp1];[tmp1][1,2] overlay=shortest=1:x=1708:y=0 [tmp2];[tmp2][1,3] overlay=shortest=1:x=3416:y=0 [tmp3];[tmp3][1,4] overlay=shortest=1:x=5124:y=0 [tmp4];[tmp4][2,1] overlay=shortest=1:x=0:y=960 [tmp5];[tmp5][2,2] overlay=shortest=1:x=1708:y=960 [tmp6];[tmp6][2,3] overlay=shortest=1:x=3416:y=960 [tmp7];[tmp7][2,4] overlay=shortest=1:x=5124:y=960 [tmp8];[tmp8][3,1] overlay=shortest=1:x=0:y=1920 [tmp9];[tmp9][3,2] overlay=shortest=1:x=1708:y=1920 [tmp10];[tmp10][3,3] overlay=shortest=1:x=3416:y=1920 [tmp11];[tmp11][3,4] overlay=shortest=1:x=5124:y=1920 [tmp12];[tmp12][4,1] overlay=shortest=1:x=0:y=2880 [tmp13];[tmp13][4,2] overlay=shortest=1:x=1708:y=2880 [tmp14];[tmp14][4,3] overlay=shortest=1:x=3416:y=2880 [tmp15];[tmp15][4,4] overlay=shortest=1:x=5124:y=2880" -vcodec libx264 -crf 18 -preset veryfast -an output.mkv