chain_overlay

# Overlay split one video into 4 and alter each - here is the youtube example https://youtu.be/bsRJNnymTxg
# I got example from this link https://ffmpeg.org/ffmpeg-all.html#Examples-126

# the command is:

ffmpeg -filter_complex "nullsrc=s=200x200 [bg]; \
testsrc=s=100x100, split=4 [in0][in1][in2][in3];\
[in0] lutrgb=r=0, [bg]   overlay=0:0     [mid0];\
[in1] lutrgb=g=0, [mid0] overlay=100:0   [mid1];\
[in2] lutrgb=b=0, [mid1] overlay=0:100   [mid2];\
[in3] null,       [mid2] overlay=100:100" -t 10 output10.MOV

# nullsrc=s=200x200 is a source for filter which ignores input data. It's size is 200x200 pixels.
# testsrc is a test video pattern
# split=4 splits the testsrc into 4 streams
# lutrgb look up table for red green blue colors
# overlay=100:0 the top left corner of the overlay video is set 100 pixels accross 0 down
# -t 10 the output video will be 10 seconds long
# output10.MOV is the finished product