Windows & macOS: Some videos aren't working, such as MP4 files, YouTube live streams, Twitch, or Vimeo

Symptoms

Some videos aren't playing on Windows or macOS, such as MP4 files, YouTube live streams, Twitch, or Vimeo.

Cause

By default, 3D WebView for Windows and macOS doesn't enable support for the proprietary H.264 video codec that is commonly used for MP4 and video streaming.

Resolution

Enable proprietary video codecs using the steps outlined in this article.