Can't access all channels when OBS in stereo mode

[erickskrauch]

What I'm trying to do:

I'm sending an SRT stream with surround 5.1 sound. In reality, it contains game audio (stereo, L R), microphone (mono C) and music (stereo Ls Rs). On the receiving side, OBS is set to stereo mode because it is supposed to output sound to the stream. OBS shows only 2 bars, but we know, that it receives 5.1 sound. By using Source Mirror from the StreamFX we can copy sounds and extract all "hidden" tracks by using the Rematrix filter. The problem is that when OBS in stereo mode, Rematrix is also can see only 2 input channels (while there are 6).

Steps to reproduce:

1. Set OBS to stereo mode.
2. Add any Media Source with 5.1 sound.
3. Add Rematrix filter to this media.
4. You can see only 2 target channels (which is correct) and 2 source channels (which isn't correct).

I don't know if it's possible to solve this on the plugin's side, since I suspect that the downmix happens inside OBS before the sound reaches the plugins. If this is the case, then consequently this problem needs to be moved to the main OBS repository.

[erickskrauch]

The response by @pkviet from Discord:

This is not fixable because filters are applied after swresample lib which resamples/downmixes or upmixes. If you set your audio to stereo, you access 2 channels downmixed from your 5.1. So rematrix has 2 channels to work with. That's normal.