long video

1. optimize source loop

ffmpeg -i w.mp4 -f lavfi -i color=gray:s=1920x1080 -f lavfi -i color=black:s=1920x1080 -f lavfi -i color=white:s=1920x1080 -preset veryslow -crf 51 -filter_complex threshold w-bwt_vslow_crf51.mp4

2. concatenate loop

for f in *.mp4 ; do echo file \'$f\' >> fileList.txt; done
&&
ffmpeg -f concat -safe 0 -i fileList.txt -c copy merged.mp4