Enable picture by picture for pre-rolls
Please enable picture by picture for pre-roll ads. I'm a small streamer and I feel a lot of people aren't willing to sit through a 30s or longer ad break just to see if my stream quality is good or chat is active or if the preview image is accurate to what I'm actually doing on stream. Picture by picture would fix this by enabling them to check out the stream and chat whilst the ad plays in the main view.

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Septeques commented
So in order to make the ad-experience better and less intrusive I propose an ad-model enabled by UEFA and other football organisations when the matches go for two 45-minute halves.
They take up the bottom of the screen, and come sliding in and thus takes the viewer's attention without ruining the viewing experience.