How to add audio to video with ffmpeg?

Question

Video

Good afternoon!
Friends, we need your help!
There is a video in mp4 format with an audio track, you need to overlay another audio on this video.
How can this be done with ffmpeg?

Answer 1

Upd. to mix the original audio from a video file with a separate audio track, and of a shorter length than the video, you will firstly have to repeat the overlay audio file, and secondly, use the amix audio filter :

ffmpeg \
-i video.mp4 \
-filter_complex "amovie=audio.mp3:loop=0,asetpts=N/SR/TB[over]; [0][over]amix=duration=shortest" \
-c:v copy \
result.mp4

Old answer, about replacing the audio track.
To replace the original audio with another one from a separate file, you need to specify both inputs, and use -map to show where to get audio and video from.
More or less like this:

ffmpeg \
-i video.mp4 \
-i newAudio.mp3 \
-c:v copy \
-c:a aac \
-map 0:v:0 \
-map 1:a:0 \
result.mp4