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I recently got a four-channel USB input device (Behringer UMC404HD). The device is working and Linux sees it; I know this because I can record four independent channels using Audacity. However, I can't work out how to ask ffmpeg to do the same thing.

If I configure ALSA and issue this command:

ffmpeg -f alsa -i pulse  test.flac

I get a stereo file that contains sound from the multichannel device that is all four channels mixed down to stereo (it's treating it as a front and rear quadraphonic source).

ffprobe on that file reports (among the mass of other info):

Stream #0:0: Audio: flac, 48000 Hz, stereo, s16

Try as I might I cannot seem to determine how to put this thing into quad mode, rather than stereo. This page looked promising, but I couldn't make any of it work for my (surely much simpler!?) case: https://trac.ffmpeg.org/wiki/AudioChannelManipulation

Anyone know how I should do this? It seems like it should be a trivial thing, and I'm probably just using the wrong words in my searches.

Tetsujin
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Toby Eggitt
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1 Answers1

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You should signal the correct number of channels on the input side, and for storing in FLAC, you will need to set a supported channel layout. So,

ffmpeg -f alsa -channels 4 -i pulse -channel_layout quad test.flac
Gyan
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