I’ve built my own synthesizer. It is likely I know much more about this subject than you suspect, even if you wish to misread what I’m talking about.

Given how audio codec compression, eg MP3 files, work it’s easy to efficiently calculate the perceived human ear loudness of a sound. The hard work’s already been done. While of course there are intricacies and edge cases, it’s not impossibly hard to match the volume level of an ad to the volume level of the content immediately preceding it. TV stations already do this, by law.

There’s also a weird undercurrent in this thread conflating audio dynamic compression with loudness. Level compression does not imply loudness. It implies a constant volume, at whatever level the engineer picks. Compress the heck out of ads if you want, then match their starting volume to the preceding volume of the streamed content, and you’re golden.