horizontal stack
ffmpeg -i input0 -i input1 -filter_complex hstack=inputs=2 -vsync 2 output

extract still frame
ffmpeg -i input -ss 00:00:00.05 -frames:v 1 output.jpg

trim video
ffmpeg -i input -ss <timestamp> -to <timestamp> -avoid_negative_ts make_zero output.mp4

map all video streams, 2nd audio stream only
ffmpeg -i INPUT -map 0:v -map 0:a:2 OUTPUT

rescale bot output videos
ffmpeg -y -i input.mp4 -vf scale=800:720:flags=neighbor output.mp4