As heard on the KTDY morning show, here is Britney Spears' Isolated Mic Feed To The Sound board, while people in the audience heard a recording.

It's a video that's been around a while but has just become a popular Youtube click, again.  Huffington Post just did a story on it, which may be the reason it's regained popularity.

The problem with the video is no one can 100% confirm it's our Louisiana girl or not.  Supposedly, she is singing into the mic while a recording plays live.  So, she's lip syncing and although her mic is not going out live to the audience, it is allegedly going back to the sound guy who is recording.

Take a listen and decide if you hear hoax.

Britney Spears' Isolated Mic Feed Is Horrible