UltraWideo

This extension resolves aspect ratio incompatibility with Ultra Wide screens. You may play 4:3 or 16:9 aspect ratio videos and they will be properly shown on 21:9 aspect ratio screens, without black side edges.

You may want to choose "Stretch mode" when you are watching some videos where a person is present in front of you as otherwise the person's forehead may be cropped...

The extension have three simple options. There's no need for complexity that some other extensions provide, it's confusing.

pause the extension
use "upscale" mode
use "stretch" mode
With these two modes, you'll be able to control any video on the web as you desire. This extension is blazingly fast, tiny build and works with any website that streams videos.

Tested and working with following video players: JW Player, VideoJS, Plyr, MediaElementJS, jPlayer, AfterGlow, HTML5 Video

Tested and working with following video embeds: YouTube, Vimeo, DailyMotion

Tested across many websites and it's not worth mentioning, the list is huge. It works literally everywhere, but to mention a few: YouTube, Vimeo, DailyMotion, Netflix... many explicit video content websites, etc.