It literally does. Audio players were implementing ReplayGain support 25 years ago.
> ad platforms would have to have multiple audio streams limited to the different loudness settings
This is trivial to solve. You have a standardized volume and a scale factor for each service. Or you use ReplayGain or similar for the same.
> it's not a hard problem in the least
No, it’s really not.
The problem with video content is there can be extended very quiet parts. If you try to bring the “average” volume of an ad to the same “average” volume as the last 30 minutes of a drama it could end up being insanely low. The average level of the drama being low due to long quiet parts.
Not always the case but this problem isn’t as simple as it might seem.
My main hope is that this doesn’t kick off a “loudness war” for tv/movie content on streaming in an effort to get its average volume up as high as the ads.
The streaming service decides where the ad breaks are. For video on demand, which is most streaming, they can precompute the ReplayGain for the 30s of video leading into the ad break.
For live video, the client can compute it.
Either way, the client can then adjust the volume of the ad to account for any difference in perceptual volume.