我的设置给你参考下，m4a格式，音质可以说算好了，20秒40k，2秒也是40k，更长时间忘了多大了，反正比上传图片流量小很多

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];