Music identifying app Shazam now valued at $1bn

You know that moment when you hear a song, and don't know what it is - you'd love to be able to buy it, but can't. There are two ways round it.

Firstly there's your own knowledge - which in many people's case is pretty dire, as we discovered when reporter Duncan Bartlett tested our presenter Dominic Laurie's music knowledge.

Thank goodness then that a few years ago a group of guys invented a piece of technology that helps you recognise a song by holding your phone up to the loudspeaker playing it.

It's called Shazam. It's grown a long way since its humble beginnings. Based in London, it's now worth a billion dollars.

It's chief executive Andrew Fisher told Dominic how it works.