How to Overlap and Merge Multiple Audio Files Using Ffmpeg

How to overlap and merge multiple audio files using ffmpeg?

acrossfade is meant to create a transition between two inputs. So, each pair of inputs has to have acrossfade applied with the result being used as an input for the next acrossfade.

ffmpeg -v debug -i file1.wav -i file2.wav -i file3.wav -filter_complex "[0:a][1:a]acrossfade=d=0.100:c1=exp:c2=exp[a01];[a01][2:a]acrossfade=d=0.100:c1=exp:c2=exp" out.wav

Edit: your inputs are 16000 Hz, and your crossfade duration is 0.1s (!), which is less than 2 audio frames at the input sampling rate. Default frame size is 1024 samples. So, frame size needs to be lowered.

ffmpeg -v debug -i file1.wav -i file2.wav -i file3.wav -filter_complex "[0:a]asetnsamples=256[0a];[1:a]asetnsamples=256[1a];[2:a]asetnsamples=256[2a];[0a][1a]acrossfade=d=0.100:c1=exp:c2=exp[a01];[a01][2a]acrossfade=d=0.100:c1=exp:c2=exp" out.wav

How to overlay/downmix two audio files using ffmpeg

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

ffmpeg - how to merge multiple audio with time offset into a video?

You have to mix the audio streams:

ffmpeg -i 1.mp4 -i 1.3gp -i 2.3gp -i 1.mp3
  -filter_complex "[2]adelay=10000|10000[s2];[3:a][1:a][s2]amix=3[a]"
  -map 0:v -map "[a]" -c:v copy result.mp4

Merge audio and video, and add an overlay on top of it with FFMpeg

It should be as simple as:

ffmpeg ... -i nature.jpg -i nature_sound.mp3 -i overlay.mp4 \
  -filter_complex [0:v][2:v]overlay ...

Merging 2 audios files with a video in ffmpeg

In order to mixdown the audio, you should use the amix filter

ffmpeg -i V.MP4 -i A1.WAV -i A2.WAV -filter_complex "[1][2]amix=inputs=2[a]" -map 0:v -map "[a]" -c:v copy Output.MP4

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