Castria finds the ads in a podcast episode and skips them. Transcribing the episode is what makes that expensive, and until now I've paid that bill for everyone. Castria 2.0 changes it: you pay in compute or you pay in money, and either way everyone listening to that show gets the result.
Most shows have exactly one listener
On my first date with my now wife, we were both shocked at how much our podcast lists overlapped. I built Castria expecting listening to be Pareto-shaped: a handful of big shows carrying most of the subscriptions, with a thin tail trailing off behind them. The popular shows have the most listeners. Obviously.
The data doesn't agree. Fewer than one in five shows on Castria has a second subscriber. Everything else has exactly one. One person, one show, one transcription bill, and nothing to spread it across.
I might still be right and just early. Castria is small enough that the curve could be forming where I can't see it yet, and overlap should get denser as more people show up. That's a reasonable thing to hope for. It isn't something to bet the architecture on.
Either way, I've been picking up that bill. That made sense while Castria was small. As it grows it's a cost I can't carry on my own, and the shape of it is counterintuitive: the listeners who cost the most are the ones bringing a long tail of shows nobody else has found yet, and those are exactly the people I want more of.
The expensive part is the transcript
To skip an ad, Castria has to know where it is. That means turning an hour of audio into text, then reading the text to work out which parts are the ad read and which parts are the show.
The reading is cheap. The transcribing is not. It's the single most expensive thing Castria does, and every new episode of every show anyone subscribes to has to go through it.
Then there's the part that surprised me: the cost tracks shows, not listeners. Ten thousand people on the same show costs the same as one person on it, because the episode gets transcribed once and everybody after that reads the same answer.
So the app gets cheaper per user as it grows. That's the good version. Here's the real one.
There were cheaper answers on the table. Cap how many shows you can follow. Only run detection above some popularity floor. Rank shows by subscriber count and let the tail wait its turn. Every one of those works, and every one of them ends with me telling you that some of your podcasts don't get ad-skip because not enough other people listen to them. I don't want to ship that.
So: two ways to pay.
Currency one: your own compute
On the free plan, your iPhone does the transcription for the shows you listen to.
Less dramatic than it sounds. Transcribing an episode isn't heavy work for a modern phone, and Castria starts on an episode as soon as it downloads. iOS is strict about background work, though, so most of it happens while you're listening. The first few minutes of a brand-new episode may play before the ad skips kick in. Castria is built so its worst day is still an ordinary podcast player with your episodes available offline.
It does cost battery. If you'd rather it didn't touch your phone at all, hand the work to a real computer. Open castria.app in Chrome or Edge, sign in, and turn on Settings → Process episodes in this tab. Leave the tab open where you can see it, and it works through your shows on that machine instead. A laptop clears a backlog a lot faster than a phone does.
Whatever your device works out doesn't stay on your device. The ad positions go back to Castria and get shared with everyone who listens to the same episode, exactly as if our servers had done it. On a show only you listen to, you are the compute. The moment a second listener shows up, your work is theirs too, and theirs is yours.
Castria 2.0 for Android is coming soon.
Currency two: money
Castria Premium is $4.99 a month or $44.99 a year, with a free month to try it. It moves the work onto our servers.
Stated plainly, that's the product: your phone stops transcribing. No battery cost, and episodes turn up with the ads already found. Premium also comes with 20 GB of cloud storage for your saved episodes, smart playlists, CarPlay, and the Apple Watch app.
What the money buys is the part I want to be clear about. It isn't a private feature. When anyone on a show has Premium, our servers handle that show's episodes for every listener on it. Subscribe, listen to something mid-sized, and you've just covered ad detection for every free listener on it. They'll never know. You mensch.
Why I think this is fair
The free plan isn't a crippled demo. It's the whole feature, ad-skip included. The only difference is which processor runs it and whose battery pays.
Nobody subsidizes a stranger's obscure show, either. If you're the only listener on something, that cost lands on you, not on a subscriber who's never heard of it. I couldn't find another way to square that one.
The part I actually like is that paying makes things better for people who don't pay. In most apps the paid tier is a wall, and your money buys you something precisely because other people can't have it. Here it runs the other direction. Every Premium subscriber makes the free plan faster and cheaper for everyone whose listening overlaps with theirs. Support your own listener community.
Which brings me back to sharing
Overlap is the one variable neither currency can buy.
Every extra person on a show is one more device that might find the ads before you press play, and one more chance someone on it has Premium. At two listeners it's a coin flip. At ten you'll rarely be the one paying. At one, it's always you.
So tell people about Castria. Not as a favor to me. Do it for the show you're currently carrying by yourself, and for whoever subscribes to it next.