[jcranmer]

> No idea if the creators opt in to this “feature” (I bet they don’t; it’s probably either all or nothing with ads), but it definitely exists.

You used to be able to opt-in to mid-roll ads. A few months ago, YouTube switched it to an opt-out system, helpfully enabling them for all then-existing videos that hadn't opted in:

> Starting in late July, videos that are longer than eight minutes will be eligible for mid-roll ads. As part of this change, mid-roll ads will be turned on for all eligible existing videos and future video uploads, including those videos where you may have previously opted out of mid-roll ads. Videos that already have mid-roll ads turned on will not be impacted.

(As I understand it, there is no way to disable the mid-roll ad on all videos, so you'd have to manually flip it for every single video. How kind of YouTube.)