AVAudioRecorder相關參數

    NSMutableDictionary *setting = [NSMutableDictionary dictionary];  
    [setting setValue:[NSNumber numberWithInt:kAudioFormatMPEG4AAC] forKey:AVFormatIDKey];//音樂格式  
    [setting setValue:[NSNumber numberWithFloat:8000.0] forKey:AVSampleRateKey];//音樂採樣率  
    [setting setValue:[NSNumber numberWithInt:1] forKey:AVNumberOfChannelsKey];//音樂通道數  
    [setting setValue:[NSNumber numberWithInt:1] forKey:AVEncoderBitRateKey];//音頻比特率  
    [setting setValue:[NSNumber numberWithInt:1] forKey:AVEncoderBitRatePerChannelKey];//標識每通道的音頻比特率  
          
    self.recorder = [[[AVAudioRecorder alloc]initWithURL:recordedFile settings:setting error:nil]autorelease];