Audio device got stuck
I'm just experiencing similar audio problems, too.
I guess it is a problem, related to a recent update since it never happened before (1 to 2 weeks on Xubuntu 20.04 LTS) and will be fixed in a coming update. Until then, following command helped me to solve the problem for some hours without restart:
pulseaudio --kill
# the same as:
# pulseaudio -k
It takes 2 to 3 seconds for pulseaudio, which will restart automatically, and often the programs, doing audioo, will work again without further intervention; sometimes I have to restart the affected programs (browser, vlc).
At least I don't have to logout or restart the computer, as YT-Videos often suggest.
I hope this helps and a real update fix will be provided soon.