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Hide the "sign-in" and cookies dialogs. Prevent the dialogs from pausing the video.
< Youtube - dismiss sign-inについてのフィードバック
Which browser are you using?
I've tried on 2 computers with chrome and firefox, and yt doesn't pause when the tab is in the background. I've tried in an incognito/private window, so no cookie is set.
This could be a browser option (eg. autoplay configuration in FF), or an extension.
Looks like yt is pausing the videos in the background tabs