#Extract Audio from video
`ffmpeg -i 'input_file' -f mp3 -ab 192000 -vn 'output.mp3'
`

#Remove Audio From Video
`ffmpeg -i 'input_video_file' -vcodec copy -an 'output_video_file'
`

#Merge audio with a video.
`ffmpeg -i video.mp4 -i audio.wav \
-c:v copy -c:a aac -strict experimental output.mp4`


#Replacing audio stream
`ffmpeg -i video.mp4 -i audio.wav \
-c:v copy -c:a aac -strict experimental \
-map 0:v:0 -map 1:a:0 output.mp4`

#Copying the audio without re-encoding
`ffmpeg -i video.mp4 -i audio.wav -c copy output.mkv`

Helpful Link: https://www.ostechnix.com/20-ffmpeg-commands-beginners/