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I have a ProRes MOV whose audio contains 8 channels of audio in a 7.1 surround layout (L R C LFE Ls Rs Lt RT).

I am preparing an H.264 MP4 for a media player that only supports AAC, and does not support 7.1, so I would like to map to 5.1, dropping ther 7th and 8th channels (Lt and Rt). Under normal circumstances I would just use the below for my transcode:

ffmpeg -i input_file -c:v libx264 -pix_fmt yuv420p -preset veryslow -crf 18 -c:a aac output_file

I've been looking at the documentation for audio layout manipulation, but am having trouble wrapping my head around it and they don't have a specific example of what I'm trying to do.

Do I need to export my audio to a WAV file first, or is there a way to manage the mapping in my transcode command? How can I map the existing first 6 channels to the new file?

dongle
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  • [This one](https://trac.ffmpeg.org/wiki/AudioChannelManipulation#a5.1stereo) is most relevant to what you're doing. Just specify the number of channels `-ac 6` to downmix. – kesh Dec 12 '22 at 20:20
  • @kesh downmixing doesn't work for me as it will impact the overall mix and separation of channels – really just need to drop them completely – dongle Dec 13 '22 at 00:30
  • Then use the `pan` filter as the linked section suggests (right below the `-ac` example) – kesh Dec 13 '22 at 02:41

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