Problem with MPEG4AAC audio format

[gdg87]

Hi, if i record with audio format MPEG4AAC the encoding doesn't work.
This is my recording settings dictionary

NSDictionary *recordSettings = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:kAudioFormatMPEG4AAC], AVFormatIDKey,
[NSNumber numberWithInt:AVAudioQualityLow], AVEncoderAudioQualityKey,
[NSNumber numberWithInt: 1], AVNumberOfChannelsKey,
[NSNumber numberWithFloat:22050.0f], AVSampleRateKey,
nil];

I need this settings because only this work with iPad Air.