Hosting services drop them in. You sign an agreement with them and they have agreement with advertisers who drop their spots into your show using DAI. Often it’s a straight up bid-system but the podcasters are not part of the process, or the podcasters can do the read and hand it over to be inserted. This means that podcasters in a lot of situations don’t actually know what ads are being run on their show.
These ads are not just not baked into the audio file, they are legitimately a mystery to the people running the show sometimes. And I think that that’s kind of unconscionable tbh. Podcasts (especially early on) owe a lot of their success to the feeling of “authenticity,” they feel more personal and less “corporate” generally. Whether that’s reality or not we can of course debate, but it’s how audiences perceived them. The reason on air reads have been generally successful for podcasts is because of the trust between the podcast and the audience that has been built over time. This runs directly counter to it.
when i use either of my podcast apps, it fetches an mp3 file (or streams it) and there's no additional ads (read this as "no additional non-native ads") that "change" when i listen again in a year. This means the podcasts that i listen to, i suppose, are not hosted on hosting platforms that inject ads. Because, as i think needs to be reiterated, podcasts are just mp3 files. you can host them with caddy, or nginx, or apache, all pointing at some file(s) in ./www/html/mp3/ One does not need to host it on "Acast" or other "podcast hosting providers", a podcast is just an mp3 file, which can be automatically fetched by anything that can download both rss and mp3 formatted files.
at a certain point, one has to ask themselves if whatever media they're ingesting is worth the scum.
It's not like the client app is inserting them.
I mean, I guess I can imagine an exceptionally-scummy podcast app, but that's not what we're talking about here.