Splits up to four videos into a grid and starts them at different timemarks using ffmpeg

splitscreen.sh

#!/bin/bash

# timestamps in trim filter can be used to sync the videos
# The duration of the first color filter specifies the length of the output video
# Scale / crop may be adjusted for the individual files
ffmpeg -i a.mp4 -i b.mp4 -i c.mp4 -filter_complex \
    "color=
        d='02\:50\:00':
        c=0x161618:
        s='1366x768'
     [placeholder];
     [placeholder]
        drawtext=
            fontfile=/usr/share/fonts/truetype/freefont/FreeMonoBold.ttf:
            text='%{pts\:hms\:-3}':
            fontcolor=0xabacad:
            x=(w-text_w)/2:
            y=(h-text_h)/2:
            shadowx=5:
            shadowy=5:
            fontsize=112
        [timestamp];
     [timestamp]
        split=4
     [t0][t1][t2][t3];
     [0:v]
        trim=
            start='00\:01\:55.8',
        setpts=PTS-STARTPTS
     [v0];
     [1:v]
        trim=
            start='00\:00\:45.6',
        setpts=PTS-STARTPTS,
        crop=1366:768:0:0
     [v1];
     [2:v]
        trim=
            start='00\:00\:40.433',
        setpts=PTS-STARTPTS,
        scale=1366:768
     [v2];
     [t0][v0]
        overlay=
            repeatlast=0
     [t0];
     [t1][v1]
        overlay=
            repeatlast=0
     [t1];
     [t2][v2]
        overlay=
            repeatlast=0
     [t2];
     [t0][t1][t2][t3]
        xstack=
            inputs=4:
            layout=0_0|w0_0|0_h0|w0_h0,
        format=yuv420p,
        fps=30
     [v]" \
     -map "[v]" output.mp4