ffmpeg filter_complex

ffmpeg
    -i vivz_nimble_guardian.mkv -i macko_nimble_guardian.mkv -i ghost_nimble_guardian_subtle_arrow_1.mp4 -i nano_nimble_guardian.mkv
    -filter_complex "
        nullsrc=size=1920x1080 [base];
        [0:v] trim=start=49.117000,setpts=PTS-STARTPTS, scale=960x540 [upperleft];
        [1:v] trim=start=50.483000,setpts=PTS-STARTPTS, scale=960x540 [upperright];
        [2:v] trim=start=42.416471,setpts=PTS-STARTPTS, scale=960x540 [lowerleft];
        [3:v] trim=start=38.100000,setpts=PTS-STARTPTS, scale=960x540 [lowerright];
        [base][upperleft] overlay=shortest=1 [tmp1];
        [tmp1][upperright] overlay=shortest=1:x=960 [tmp2];
        [tmp2][lowerleft] overlay=shortest=1:y=540 [tmp3];
        [tmp3][lowerright] overlay=shortest=1:x=960:y=540[v]
    "
    -map "[v]" -map 1:a -c:v libx264 -shortest output.mkv