How to overlay/downmix two audio files using ffmpeg

Question

Can I overlay/downmix two audio mp3 files into one mp3 output file using ffmpeg?

Answer 1

stereo + stereo → stereo

Normal downmix

Use the amix filter:

ffmpeg -i input0.mp3 -i input1.mp3 -filter_complex amix=inputs=2:duration=longest output.mp3

Or the amerge filter:

ffmpeg -i input0.mp3 -i input1.mp3 -filter_complex amerge=inputs=2 -ac 2 output.mp3

Downmix each input into specific output channel

Use the amerge and pan filters:

ffmpeg -i input0.mp3 -i input1.mp3 -filter_complex "amerge=inputs=2,pan=stereo|c0<c0+c1|c1<c2+c3" output.mp3

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mono + mono → stereo

Use the join filter:

ffmpeg -i input0.mp3 -i input1.mp3 -filter_complex join=inputs=2:channel_layout=stereo output.mp3

Or amerge:

ffmpeg -i input0.mp3 -i input1.mp3 -filter_complex amerge=inputs=2 output.mp3

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mono + mono → mono

Use the amix filter:

ffmpeg -i input0.mp3 -i input1.mp3 -filter_complex amix=inputs=2:duration=longest output.mp3

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More info and examples

See FFmpeg Wiki: Audio Channels

Answer 2

Check this out:

ffmpeg -y -i ad_sound/whistle.mp3 -i ad_sound/4s.wav -filter_complex "[0:0][1:0] amix=inputs=2:duration=longest" -c:a libmp3lame ad_sound/outputnow.mp3

I think it will help.

Answer 3

The amix filter helps to mix multiple audio inputs into a single output.

If you run the following command:

ffmpeg -i INPUT1 -i INPUT2 -i INPUT3 -filter_complex amix=inputs=3:duration=first:dropout_transition=3 OUTPUT

This command will mix 3 input audio streams (I used two mp3 files, in the example below) into a single output with the same duration as the first input and a dropout transition time of 3 seconds.

The amix filter accepts the following parameters:

• inputs: The number of inputs. If unspecified, it defaults to 2.

• duration: How to determine the end-of-stream.

  • longest: The duration of the longest input. (default)

  • shortest: The duration of the shortest input.

  • first: The duration of the first input.

• dropout_transition: The transition time, in seconds, for volume renormalization when an input stream ends. The default value is 2 seconds.

For example, I ran the following command in Ubuntu: FFMPEG version: 3.2.1-1 UBUNTU 16.04.1

ffmpeg -i background.mp3 -i bSound.mp3 -filter_complex amix=inputs=2:duration=first:dropout_transition=0 -codec:a libmp3lame -q:a 0 OUTPUT.mp3

-codec:a libmp3lame -q:a 0 was used to set a variable bit rate. Remember that, you need to install the libmp3lame library, if is necessary. But, it will work even without the -codec:a libmp3lame -q:a 0 part.

Reference: https://ffmpeg.org/ffmpeg-filters.html#amix