Have a Mac and having trouble with MP4?
I wrote my first extension and posted it to the Chrome store... It is for the Mac users and for some Late Model macs where MP4 files won't play (Some news sites, youtube, etc.) and require refreshing of the page or quite often videos won't play. By installing the extension, it resolves some, but not all issues as some sites only offer MP4.
The extension borrows heavily from the h264ify project, but applies to all websites and will strip out the ability to play mp4 in hopes that the site will send vp8, vp9, webm, or flash (yuck, but better than nothing). This extension is meant to be a bandaid and will help Vivaldi run a little bit better until the issue can be resolved.