Pay per play or net audio adds

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Well i am making a website and my friend told me that if there is alot of traffic i could earn money, apparentyl what happends is that you put a code on your website and register with them, then when anyone visits your website a 5 second ad plays and you get payed for it? im jsut wondering if anyone knows anyhting so i wont waste my time... cheers, happy mylottting :)