I imagine that encoding the ads into videos would be too expensive. Ads change often and are personalized, so the video streams would also need to be personaliz

I imagine that encoding the ads into videos would be too expensive. Ads change often and are personalized, so the video streams would also need to be personalized and couldn't be cached and served from a simple edge CDN anymore. Instead each ad is it's own stream which is loaded (or in this case, not loaded, so instead of blocking playback entirely it just skips the ad).