[FFmpeg-user] Transcoding multichannel audio to AAC failing

[Ruane, Tom]

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

Thanks.


******************************************************************************************************************
Experience the British Library online at www.bl.uk<http://www.bl.uk/>
The British Library’s latest Annual Report and Accounts : www.bl.uk/aboutus/annrep/index.html<http://www.bl.uk/aboutus/annrep/index.html>
Help the British Library conserve the world's knowledge. Adopt a Book. www.bl.uk/adoptabook<http://www.bl.uk/adoptabook>
The Library's St Pancras site is WiFi - enabled
*****************************************************************************************************************
The information contained in this e-mail is confidential and may be legally privileged. It is intended for the addressee(s) only. If you are not the intended recipient, please delete this e-mail and notify the postmaster at bl.uk<mailto:postmaster at bl.uk> : The contents of this e-mail must not be disclosed or copied without the sender's consent.
The statements and opinions expressed in this message are those of the author and do not necessarily reflect those of the British Library. The British Library does not take any responsibility for the views of the author.
*****************************************************************************************************************
Think before you print