[FFmpeg-user] Audio mapping and mixing

[Paul B Mahol]

On Sun, Jun 9, 2024 at 6:51 PM Media Mouth <communque at gmail.com> wrote:

> Following up on an earlier post "amix vs amerge / how to" but now testing
> on ffmpeg version 7.0.1
>
> The overall goal here is to learn how (if possible) to take source files
> with 10 - 20 audio channels and mixdown / assign those in various ways to
> -- 2 channel, 4 channels etc etc -- it depends on the who's requesting the
> mixdown.
>
> I've been testing with -filter_complex amix, amerge, and join.  I'm not
> yet sure which is most suitable to the task or whether there are better
> FFmpeg approaches altogether.
>
> If the goal is to take a source with lots of audio streams and mix those
> down in any combo, how could that be achieved?
> According to the FFmpeg documentation amix "Mixes multiple audio inputs
> into a single output <https://ffmpeg.org//ffmpeg-filters.html#amix>",
> which suggests amix is not the best choice?
> One post I read suggested 'join' provided more control & flexibility than
> both 'amerge' and 'amix', so I've been testing with that
>
> I made some progress, but not yet doing mixdowns.  Simply assigning to
> input streams to the same output track generates an error...
>
> ffmpeg -i SoundTestIn.mxf \
> -filter_complex
> 'join=inputs=4:channel_layout=stereo:map=0.0-FR|1.0-FR|2.0-FL|3.0-FR' \
> SoundTestOut.mov
>
> Error: Multiple maps for output channel 'FR'
>
> Perhaps join is NOT the best approach?  Thanks for any insights here.
>

Study documentation of following audio filters in FFmpeg:

amix
join
amerge
channelsplit
channelmap
pan

Will need to use at least 2 filters from above list each time in single
(complex) filtergraph to do actual job.


>
>
>
> full output
>
> ffmpeg version 7.0.1 Copyright (c) 2000-2024 the FFmpeg developers
>   built with Apple clang version 15.0.0 (clang-1500.3.9.4)
>   configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/7.0.1
> --enable-shared --enable-pthreads --enable-version3 --cc=clang
> --host-cflags= --host-ldflags='-Wl,-ld_classic' --enable-ffplay
> --enable-gnutls --enable-gpl --enable-libaom --enable-libaribb24
> --enable-libbluray --enable-libdav1d --enable-libharfbuzz --enable-libjxl
> --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist
> --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libssh
> --enable-libsvtav1 --enable-libtesseract --enable-libtheora
> --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx
> --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2
> --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype
> --enable-frei0r --enable-libass --enable-libopencore-amrnb
> --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex
> --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack
> --disable-indev=jack --enable-videotoolbox --enable-audiot
>  oolbox --enable-neon
>   libavutil      59.  8.100 / 59.  8.100
>   libavcodec     61.  3.100 / 61.  3.100
>   libavformat    61.  1.100 / 61.  1.100
>   libavdevice    61.  1.100 / 61.  1.100
>   libavfilter    10.  1.100 / 10.  1.100
>   libswscale      8.  1.100 /  8.  1.100
>   libswresample   5.  1.100 /  5.  1.100
>   libpostproc    58.  1.100 / 58.  1.100
> [Parsed_join_0 @ 0x600003df4000] Multiple maps for output channel 'FR'.
> [AVFilterGraph @ 0x6000021f0000] Error initializing filters
> Failed to set value
> 'join=inputs=4:channel_layout=stereo:map=0.0-FR|1.0-FR|2.0-FL|3.0-FR' for
> option 'filter_complex': Invalid argument
> Error parsing global options: Invalid argument
>
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