With Void being a rolling release a lot is not tested. A build script just builds everything and uploads to the repo. Voids mozplugger seems to be built with mp4/webm disabled, and doesn't work with embedded audio/video. You audio issue is because the latest pulseaudio broke as well. The only way I've found to get YouTube in Void is by installing gtk-straw-viewer. It's a front end for invidious. The only issue with that is that invidious servers keep getting shut down, so you have to edit the config quite often to update the server address. There also is no package for browser-plugin-vlc in void. If YouTube is important to you I'd suggest something debian based that has proper vlc and mozplugger support.
Cheers