Most of the times when your friends get music or video on USB they are of different format from the supported ones. AAC which is the audio format for apple devices like iPad, iPod and iPhone and MPEG4 is one of the most common video format are not directly supported but if you download the Optional Media Update from XBox live and schedule it to download on your Xbox you will be able to play them easily.
In case you dont have it, when you try to play any music format like this, Xbox console will prompt and download the codex for you at that very moment. But I would suggest you to download this right now so you can play it anytime without the internet also.
Apart from this here is the list of Video formats supported by XBox 360 :
|From USB storage device to Xbox 360 Dashboard Video Player||WMV(Unprotected),|
|From Windows Media Player 11 to Xbox 360 Dashboard Video Player||WMV(Protected)|
|From the Zune software to the Xbox 360 Dashboard Video Player||WMV(Unprotected)|
|From Windows Home Server to the Xbox 360 Dashboard Video Player||WMV (protected)|
|From Windows Media Center to an Xbox Media Center Extender||WMV (protected)|