Replace audio

ffmpeg -i video.mp4 -i audio.wav -map 0:v -map 1:a -c:v copy -shortest output.mp4

• The -map option allows you to manually select streams / tracks. See FFmpeg Wiki: Map for more info.
• This example uses -c:v copy to stream copy (mux) the video. No re-encoding of the video occurs. Quality is preserved and the process is fast.
  • If your input audio format is compatible with the output format then change -c:v copy to -c copy to stream copy both the video and audio.
  • If you want to re-encode video and audio then remove -c:v copy / -c copy.
• The -shortest option will make the output the same duration as the shortest input.

Add audio

ffmpeg -i video.mkv -i audio.mp3 -map 0 -map 1:a -c:v copy -shortest output.mkv

• The -map option allows you to manually select streams / tracks. See FFmpeg Wiki: Map for more info.
• This example uses -c:v copy to stream copy (mux) the video. No re-encoding of the video occurs. Quality is preserved and the process is fast.
  • If your input audio format is compatible with the output format then change -c:v copy to -c copy to stream copy both the video and audio.
  • If you want to re-encode video and audio then remove -c:v copy / -c copy.
• The -shortest option will make the output the same duration as the shortest input.

Mixing/combining two audio inputs into one

Use video from video.mkv. Mix audio from video.mkv and audio.m4a using the amerge filter:

ffmpeg -i video.mkv -i audio.m4a -filter_complex "[0:a][1:a]amerge=inputs=2[a]" -map 0:v -map "[a]" -c:v copy -ac 2 -shortest output.mkv

See FFmpeg Wiki: Audio Channels for more info.

Generate silent audio

You can use the anullsrc filter to make a silent audio stream. The filter allows you to choose the desired channel layout (mono, stereo, 5.1, etc) and the sample rate.

ffmpeg -i video.mp4 -f lavfi -i anullsrc=channel_layout=stereo:sample_rate=44100 \
-c:v copy -shortest output.mp4

Also see

• Combine two audio streams into one
• FFmpeg Wiki: Audio Channel Manipulation
• FFmpeg mux video and audio from another video