Can not choose MFI speakers to play while recording?

Hi friends,

I met this problem while my app was recording to get the Sound level trough iPhone's mic: I can only choose the speaker of iPhone, without the airplay-able speakers in my network.

It happens when i start the audio session like following:

VAudioSession * audioSession = [AVAudioSession sharedInstance];

[audioSession setCategory:AVAudioSessionCategoryPlayAndRecord error:&error];

I use MPMoviePlayerController to play an audio file. And i need play this audio on a specail airplay device.

Do any body can help me? Thanks very much.