I'm listening to a podcast from the BBC, which says "this podcast is supported by advertising outside of the UK" and then plays an ad.

Except the ads have all been specifically for Australia. I assume they're not just spamming all listeners with ads for Australian banks, but then my question is this:

How do they know to send Australian ads to my podcatcher?

How do they insert specialised advertising part-way into an mp3 file?

So the BBC has partnered with a company called Acast, which claims:

"Acast’s sophisticated, contextual targeting uses dynamic insertion technology—which we invented—so brands can reach the right audience, in the right way, at the right moment, as many times as they require."

So the ads are inserted at the time of download, rather than at the time of production (the selling point of this being that a podcast's back catalogue can include modern ads).

One of my main issues with this is: I sure hope the BBC has an archiving plan in place.

It's highly likely that Acast will go out of business before the BBC stops producing podcasts. What will happen to these downloads then? Will they still work, or will everything break?