I decided to do a quick setup of headless plexamp on a spare Pi 3 for a simple hdmi player to use on home thater systems.
I did some initial testing a while back and had success, although my test run didn’t do thorough testing as once I proved the concept, I moved on to a Pi5 and a DAC.
Shifting back over to this, I find my initial testing on quadraphonic files overlooked something. When I playback 5.1 material today, although my receiver shows receiving a 5.1 signal, I’m finding the center channel appears to be dropped - no vocals coming out of my test playback.
My receiver doesn’t actually have a center speaker connected and is relying on downmixing to a phantom center, but I’ve thoroughly tested this is working as expected.
When playing the same file out my desktop PC to the same receiver, the receiver shows receiving a 5.1 source, that is outputting to 4.0, and I hear the vocals. But when I use my Pi3, playback the same file using plexamp, the receiver shows receiving 5.1 that is outputting to 4.0, but I receive no vocals.
The Pi3 absolutely is not outputting the vocal channel on the center channel - it’s a silent center.
All downmixing options are turned off, so it should be outputting the pure 5.1 mix as is, and my receiver should be receiving audio on the center that it downmixes to the fronts.
I did a quick playback test and grabbed the log for analysis.
I have confirmed this behavior to persist on a Pi4.
My Pi5 with hifiberry DAC8X configured to mixdown center to phantom center in fronts works, which suggests plexamp does have a channel assignment correct. But I am finding consistently, in a Pi3 and Pi4 using the hdmi outputs (by way of setting plexamp to use default output and configuring the hdmi as the default output in the OS), the receiver detects a 7.1 output (I am playing 5.1 content, and my receiver is configured to output 5.1 and 7.1 content as 4.0, and has been proven to consistently do this correctly with a phantom center), and plays back the front channels out the front, the rear channels out the rear, but the center is lost. No vocals in my test playback, which are isolated to the center channel.
I recall that in testing on my Pi5, in plexamp settings, I could select the hdmi output directly instead of default, and that would work (been a while since I did this, and didn’t test this extensively), so this led me to believe I could do the same with the 3 and 4. But I am finding if I select the HDMI output directly from plexamp, playback is unable to complete, it just doesn’t playback. It doens’t appear to try to playback, just fails to playback without error.
If either plexamp could be fixed to output directly to the HDMI ports of a Pi3 or Pi4, or if we could figure out the proper configuration for a 5.1 mix to output the hdmi properly when being used as the default output of a Pi, that would be great, as figuring one of these options out will be necessary in order for plexamp headless to be a viable player on an hdmi home theater.
I fail to understand the concept of creating a Pi app that has so many compatibility issues with the Pi, the hardware it was supposedly designed to work with…
