I have found the solution myself.
Apparently, If you install Windows 10 Pro N, media playback isn't supported.

You need this extra feature from Windows 10.
https://support.microsoft.com/en-us/topic/media-feature-pack-for-windows-10-n-october-2020-2f992f23-1fca-60a3-9907-fd4fe896a8a7

Thanks for the support!

@Gwen-Dragon This is the link to update the Media Feature Pack in case anybody needs https://www.microsoft.com/en-us/software-download/mediafeaturepack.

@matir143 said in Vivaldi cannot play some videos on Windows:

Chrome, there everything works.

I have Windows 10 N version that comes with no media support.

So Chrome has inbuilt set of (full) media support!?
Obviously we will have to remember that when trouble-shooting/comparing browsers!!

@Hadden89 Thanks, I know I should update and I will. Thanks all for confirming.

Nun, ich hab nun des Rätsels Lösung. Auf meinem Rechner ist die Enterprise N Version von Windows 10 drauf. Wenn man das dazu passende Windows Media Pack installiert (command line --> winver eingeben) dann gehts plötzlich auch mit vivaldi.

https://www.microsoft.com/en-us/software-download/mediafeaturepack

@xyzzy said in Vivaldi won't reproduce some YouTube videos:

vivaldi://flags

I'm always on the latest snapshot, and I can play the videos on the site. What doesn't work for me is Twitter and (I just discovered this) Gamespot. Youtube, Vimeo and the likes are fine.

Gwen-Dragon's advice worked for me! I went to the first github link (above), copied the latest-proprietary-media.sh script to a local directory and executed it from my account (not root) with no problems. After re-starting Vivaldi and checking the link where the test videos live (you get a reminder with the link when the script completes) the sites that had not worked for me before do now.

Of course, I still hate auto-start videos... 😉

@Stormbolter Do you have any extensions installed?

@doctorg

on vivaldi 4.1 it is absolutely fine. Furthmore, my other media players have not been crashing 🙂