如何使用AVAudioRecorder录音 如下：

// 录音存储的url

NSURL *fileUrl = [NSURL fileURLWithPath:@"/Users/midas/Desktop/sounds.m4a"];

NSMutableDictionary *dict = [NSMutableDictionary dictionary];

// 采样率

[dict setObject:@44100.0f forKey:AVSampleRateKey];

// 编码格式

[dict setObject:@(kAudioFormatAppleLossless) forKey:AVFormatIDKey];

// 声道数目

[dict setObject:@1 forKey:AVNumberOfChannelsKey];

// 质量

[dict setObject:@(AVAudioQualityLow) forKey:AVEncoderAudioQualityKey];

_recorder = [[AVAudioRecorder alloc] initWithURL:fileUrl settings:dict error:nil];

// 录制5s

[_recorder recordForDuration:5];

[_recorder prepareToRecord];

// 开始录制

[_recorder record];