I’m not talking about the player or the controls being server-side. I’m talking about the player being locked into a streaming mode where it does nothing but stream the ads. After the ads are streamed, the player returns to normal video mode and the server sends the actual video data.

This means no metadata about the ads are required on the player side about the ads.

Sure you can hack the player into not being locked during the streaming of the ads. But that won’t get you very far, since it’s a live stream. You can’t skip forward, because the data isn’t sent yet. You can skip backwards if you’d like, with what’s in the current buffer, but why would you want to? You can have the player not display the ads, but that means staring at a blank screen till the ads are over. And that’s always the case, one can simply walk away during the ads, that’s always been the case.

Technically I can think of several ways to implement this, without the client having meta data about the ads. And with little to none ways of getting around the ads. Once the video starts it’s business as usual, so it doesn’t impact regular viewing.

and making them server site, while possible would introduce tremendous amounts of lag, and put that much more load on the servers. Imagine a server that has to handle playback of billions of users all at once. That’s probably quite a bit worse than most average, or even high-level DDoS attacks.