[FFmpeg-user] Transcoding multichannel audio to AAC failing

Ruane, Tom Tom.Ruane at bl.uk
Thu Oct 6 18:54:46 EEST 2022

I’m having issues transcoding multichannel audio between formats.

Depending on the source material I either define a speaker layout/channel order and write that into the FMT chunk of an RF64 .wav (e.g. L R C) or leave the order undefined, with the intention of it being treated as multi-mono (channel: 1, 2, 3, 4, 5 etc.).

On conversion to AAC .m4a, FFMPEG either recognises there is a channel order and maps an equivalent from its standard list of mappings (sometimes a match, sometimes not), or fails conversion when the channels do not correlate to its own mappings - for example anything between 8 and 16 channels fail to transcode.

Is there a way to prevent FFMPEG applying its own channel-mapping when transcoding between formats (particularly AAC)?  Is there any way to transcode non-typical multichannel audio (9 channels / 8.1)?
Command: ffmpeg.exe -i example.wav -acodec aac example.mp4


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