音频用什么压缩格式

NSMutableDictionary* recordSetting = [NSMutableDictionary dictionaryWithObjectsAndKeys:

                                          [NSNumber numberWithInt:kAudioFormatMPEG4AAC], AVFormatIDKey,
                                          [NSNumber numberWithFloat:44100.0], AVSampleRateKey,
                                          [NSNumber numberWithInt:1], AVNumberOfChannelsKey,
                                          [NSNumber numberWithInt:AVAudioQualityMin], AVEncoderAudioQualityKey,
                                          [NSNumber numberWithInt:AVAudioQualityMin], AVSampleRateConverterAudioQualityKey,
                                          [NSNumber numberWithInt:8], AVLinearPCMBitDepthKey,
                                          nil];