There's various companies that do this for you as a service, including verifying the reach across market research panels. If you want a fairly raw build-your-o

There's various companies that do this for you as a service, including verifying the reach across market research panels. If you want a fairly raw build-your-own solution you could speak to someone like TVEyes who'll give you an mpeg or mp3 feed from 100s of channels across the USA. If you insert a fingerprint into your advert audio, you can then auto-detect plays across the entire country.