I have one command which has some issues. if one video have shorted length then second video. first video will pause and second will continue to play. other issue is that this command is very slow
ffmpeg -i vid1.mp4 -i Vid2.mp4 -filter_complex "[1:0] setsar=sar=1,format=rgba [1sared]; [0:0]format=rgba [0rgbd]; [0rgbd][1sared]blend=all_mode='addition':repeatlast=1:all_opacity=1,format=yuva422p10le" -c:v libx264 -preset slow -tune film -crf 19 -c:a aac -shortest result.mp4