Split/clone HDMI/Headphone Audio?

[ParadoxGBB]

Hello,

There's been a change in Raspberry Pi OS that changes how audio is handled that's been discussed here tons, and I'm not going to relitigate here, but it might be contributing to what I'm experiencing.

My setup is a RPi4, and I connect to one HDMI output to a TV and another with composite/headphones output snaked to a bluetooth transmitter to noise-cancelling earphones. What I appreciate is the flexibility of having both audio sources play and having only one powered on at a given time (mute the TV, or power off the transmitter), and not having to go through software options each time.

Kodi does this very well on the Pi, they have the option:
<setting id="audiooutput.audiodevice">PI:Both</setting>

And that works great.

I could have sworn since the kernel updates last year that I had the same experience with mirrored audio output for ES / emulators as well, but that might not be the case. I tried setting the legacy compatibility settings in boot.txt as documented but could not get that working, so I could be incorrect on that.

Anyone know if it's possible to fork audio output on both HDMI and headphones? I'm not as linux savvy as others here, so apologies if this is a newbie question.

I currently have the settings as "HDMI" in audio settings and

Device: Default
Card: HDMI
OSX: ALSA

For emulationstation.

Thanks in advance!

-=G=-

[mitu]

There is some configuration that can be done by modifying the ALSA configuration file ($HOME/.asoundrc), but looks complicated and there's no 'one-size-fits-all' solution (depends on the devices present on the system).

You could try installing PulseAudio and configure the module-combine for simultaneous output.