FFMPEG - convert video to Black & White with threshold?
Use the threshold filter:



ffmpeg -i main_1280x720.mp4 -f lavfi -i color=gray:s=1280x720 -f lavfi -i color=black:s=1280x720 -f lavfi -i color=white:s=1280x720 -filter_complex threshold output.mkv


This filter requires four video streams to perform thresholding:


main input
threshold
min
max


You can optionally add the format filter for a grayscale pixel format: threshold,format=gray (assuming your output format supports that otherwise additional pixel format conversion will automatically take place).