VLC setting volume from command line/bash
Seems to be a known bug. Volume option doesn't have any effect
For anyone that comes by this later, I had to disable the "Save audio" option under the audio settings for this to work. I also had to use one of the other audio settings. Mine was:
--mmdevice-volume=<float [0.000000 .. 1.250000]>
Other options are
--directx-volume=<float [0.000000 .. 2.000000]>
--waveout-volume=<float [0.000000 .. 2.000000]>