CODEWITHSUNDEEP
audioffmpegmergelibavchannel
xtingray
xtingray

Reputation: 503

How to merge several audio files using Libav API?

Currently, I am implementing a new feature of my software using the Libav API. This is the requirement: to merge a list of audio files (MP3 and WAV) and create a unique audio file (MP3) as output. Note: The challenge is not about concatenating files, but merging them. When the output sound is played, all the input audio content must sound at the same time, as when you merge several files in a video editor.

I was researching about Libav audio streams, and I am just guessing that my requirement is related to the "channels" concept, I mean, that there is possible to include several audios in the stream, using one channel per audio or something like that. I was hoping to find more information about this topic, but FFmpeg/Libav documentation is actually scarce.

Right now, I am able to merge several audio streams to a video stream successfully and I can create a playable MP4 file. My problem is that players like MPlayer/VLC only reproduce the first audio stream with the video, the other two audio streams are ignored.

I was looking at the set of examples included in the FFmpeg source code, but there is nothing specifically related to my requirement, so I would appreciate any source code reference or algorithm explanation about how to merge several audio files into one using libav. Thanks.

Update:

The ffmpeg command to merge several audio files requires de filter flag "amix", like in this example:

ffmpeg -i 1.mp3 -i 2.mp3 -i 3.mp3 -filter_complex amix=inputs=3:duration=first result.mp3

All the syntax related to this option is described in the FFmpeg Documentation

Checking the FFmpeg source code, it seems the amix feature implementation is included in the file af_amix.c

I am not 100% sure, but it seems the general algorithm is described in the function:

static int activate(AVFilterContext *ctx)

Upvotes: 0

Views: 996

Answers (2)

xtingray
xtingray

Reputation: 503

This C example gets two WAV audio files and merges them to generate a new WAV file using ffmpeg-4.4 API. Tip: The key of the process is to use these filters: abuffer, amix and abuffersink.

https://github.com/xtingray/audio_mixer/

Although it doesn't support MP3 format as the output, it gives you the basics to understand how to implement your own requirements. I hope it can be handy for anyone looking for references about this specific topic.

Upvotes: 0

kesh
kesh

Reputation: 5463

Do you know how to merge several audio files using command line ffmpeg? It would help you if you first understand how to do it with the ffmpeg command then reverse engineer how it achieves it. It's all about how to constrct a filtergraph and pass data through it.

As for examples, check out examples/filter_audio.c and examples/filtering_audio.c

Upvotes: 1

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