FFmpeg - Add silence sound to video so you can upload it to Youtube

# Ignore existing audio of video.
ffmpeg -y -nostdin -f lavfi -i anullsrc -i INPUT_VIDEO.mp4 -shortest -c:v copy \
            -c:a aac -map 0:a -map 1:v OUTPUT_VIDEO.mp4
 
# or Add silent sound to video.
ffmpeg -f lavfi -i anullsrc=channel_layout=stereo:sample_rate=44100 \
            -i INPUT_VIDEO.mp4 -shortest -c:v copy -c:a aac OUTPUT_VIDEO.mp4