Hi,
I’m running the Snap of Retroarch on Ubuntu 18.04 (Unity desktop) on a Core i3 system hooked up to my television.
Sound does not work anywhere within Retroarch (no clicks when moving through the main menu and no sound in ROMs - tried multiple cores: NES, SNES, PC Engine, N64…).
Launching Retroarch from the terminal, I get the following error:
ALSA lib seq_hw.c:457:(snd_seq_hw_open) open /dev/snd/seq failed: Operation not permitted
Is this perhaps related to the Snap package being sandboxed? 
The sound is output over HDMI on an NVIDIA GeForce 750 Ti and is working fine elsewhere in the system (web browsers, Kodi, VLC, etc.). I’m using nvidia-driver-415.
I’ve tried both the deb from the Libretro PPA as well as the Flatpak but both had issues recognizing input - to move through the RA menu, I had to mash the arrow key 8-10 times for each movement (something weird bug related to polling?). Input works as expected in the Snap version, but there’s no sound.
Under Settings > Audio > Devices, I have no devices available to choose from (it’s blank). This is also the case on my laptop, though, and sound is working fine there (using deb version).
That said, I followed the suggestion here and tried every device listed in the output of aplay -L to no avail. I can post that output if anyone would find it helpful, but I’m thinking it’s a dead end.
I’ve been beating my head against this issue for a few weeks now and I’m running out of ideas - I’d really appreciate it if someone could point me in the right direction!