Audio downmixing on multichannel sources

[Katzenwerfer]

Originally posted this on the GitHub repository's discussions page, but was told to move it over here as it was very likely to be a support related question.
I was curious if there is any downmixing being down when trying to capture a surround source through the application capture feature.
So far, I've been unable to figure this out since games mix audio in some odd ways, but to my knowledge any extra channels are just skipped entirely unless you have surround audio enabled.

 

[AaronD]

My experience with multichannel physical interfaces - specifically digital mixing consoles for live concerts and such, that also have a multitrack USB sound card built-in - is that OBS takes whatever channel count it gets from the device, *and mixes down the entire device* to whatever channel count OBS is set for. THEN it gives you that downmix as a single worthless source.

If it's set to stereo, for example, and you have a 32-channel console with 30 mics and a stereo final mix, OBS puts all of the odd channels on the left, even on the right, and gives you a muddled mess of all the mics like that, in addition to the final mix, and you can't do anything about it except to go into the console's settings and make all of its USB sends silent except for the ones you actually want.

I would not be surprised if other sources do the same thing. I suppose it's possible that it figures out to downmix 6 channels as 5.1 into stereo, with the center going to both sides and maybe the sub too, but I wouldn't count on it. It may still take it as 3 stereo pairs to just mash together.

If you really want to control how your audio works, use a DAW for all of it, and bring the final result into OBS to pass through unchanged.

 

[rockbottom]

Maybe....

⚠ IMPORTANT WARNING: make sure to select the same channel layout as your input (if you have a 4.1 audio source do not select 7.1). If you don't, channel mixing may (or may not) occur. There is an automatic channel rematrixing when either downmixing or upmixing is mandated by a difference in channel layouts between source and output. This channel rematrixing mixes channels in general. Or it can remove a channel (ex: 3.1 source to 4.0 output removes the LFE channel).

Dolby: Streams can be encoded in ac3/eac (using Output > Advanced > Custom FFmpeg recording > stream to URL). But support of the various streaming services or web players has not been tested. Capture of Bolby can be tricky if the channels are lumped into two PCM channels; in order to be decoded correctly and encoded all the channels should be held in different PCM channels.

Surround Sound Guide | OBS

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