Feature Request: Add option to reduce quality when window loses focus

[thejavascriptman]

Feature Description:
Please consider adding an additional option to reduce playback quality when window loses focus.

Reason:
On many configurations video playback uses a lot of CPU due to hardware decoding not being used, this usually happens on Linux and even on Windows when the user is forced to disable hardware decoding due to buggy video drivers.

How would it work?
Basically when a video is being played while the respective browser window is focused, quality setting should work as it is working right now, however if the browser loses focus (i.e. if it's being minimized or another window gains focus), quality could go down to 360p, so processor usage would be lower (if the option is enabled)

Possible issues:
I understand that some buffering could happen when switching focus, but IMHO that's a worthy tradeoff for this kind of feature

Sample mockup:

[Alpaczyk]

Hi, I would like to work on it @thejavascriptman @ImprovedTube

[ImprovedTube]

thank you @Alpaczyk, great choice!

On many configurations video playback uses a lot of CPU

Dont bandwidth & cpu go down at all for background playing? @thejavascriptman

Possible issues:
I understand that some buffering could happen when switching focus, but IMHO that's a worthy tradeoff for this kind of feature

In theory it could delay switching quality until buffer is empty. (are buffer features history yet? #581)
Instead we could work with a timer like 10 seconds without going back to the tab, or any value the user sets.
and minimum remaining video duration like 20 seconds. (and low quality from the start if another video starts afterwards.)

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Similar:

#2239