It seems that one or the other seems to lock onto ALSA.
If I play a youtube video first, and keep the browser tab open, VLC won't play any audio. Same thing vice versa. I often watch shows and browse forums, sometimes pause the show and watch the quick video, but it's difficult with this issue. It's probably a quick fix, but I can't find anything.
Are you using only ALSA to play sound?
Do you have any mixers installed? It can be, if there no mixer available in the system.
install it, all look there:
https://wiki.archlinux.org/index.php/Ad … k_problems