No sound when playing videos on raspberry box

I’ve recently got my raspberry box and configured it with the official image for raspberry pi 3 and I love it
I’m just having a little issue with playing videos in browsers. It works on chrome but with no sound.

I reckon this is a problem in my operating system though not in raspberry pi. Because I went to try nextcloud demo in the official website and I encounter the same problem, no sound.

Am I right? anyone had this problem and solved it?

Nextcloud box: nextcloud 11.0.4
OS: KDE neon 5.10
Sound backend: VLC

Im also fighting with this issue. It would maybe help to know if its a browser issue or an OS issue (not supporting the codec).