• 先用 AVAudioRecorder 录音生成 wav格式音频
• 用lame将wav格式转换成mp3

- (void)recordAudio
{
    AVAudioSession *audioSession = [AVAudioSession sharedInstance];
    [audioSession setCategory:AVAudioSessionCategoryRecord error:nil];

    NSError *error = nil;
    audioRecorder = [[ AVAudioRecorder alloc] initWithURL:[NSURL URLWithString:[self getAudioFilePath]] settings:[self audioRecordingSettings] error:&error];
    audioRecorder.meteringEnabled = YES;

    if ([audioRecorder prepareToRecord] == YES)
    {
        audioRecorder.meteringEnabled = YES;
        [audioRecorder record];
    }
    else 
    {
        NSLog(@"录音失败");
    }
}

- (void)convertToMp3
{
    NSString *mp3FilePath = [self getMp3FilePath];
    
    @try {
        int read, write;
        
        FILE *pcm = fopen([[self getAudioFilePath] cStringUsingEncoding:1], "rb");  //source 被转换的音频文件位置
        fseek(pcm, 4*1024, SEEK_CUR);                                   //skip file header
        FILE *mp3 = fopen([mp3FilePath cStringUsingEncoding:1], "wb");  //output 输出生成的Mp3文件位置
        
        const int PCM_SIZE = 8192;
        const int MP3_SIZE = 8192;
        short int pcm_buffer[PCM_SIZE*2];
        unsigned char mp3_buffer[MP3_SIZE];
        
        lame_t lame = lame_init();
        lame_set_in_samplerate(lame, 11025.0);
        lame_set_VBR(lame, vbr_default);
        lame_init_params(lame);
        
        do {
            read = fread(pcm_buffer, 2*sizeof(short int), PCM_SIZE, pcm);
            if (read == 0)
                write = lame_encode_flush(lame, mp3_buffer, MP3_SIZE);
            else
                write = lame_encode_buffer_interleaved(lame, pcm_buffer, read, mp3_buffer, MP3_SIZE);
            
            fwrite(mp3_buffer, write, 1, mp3);
            
        } while (read != 0);
        
        lame_close(lame);
        fclose(mp3);
        fclose(pcm);
    }
    @catch (NSException *exception)
    {
        NSLog(@"%@",[exception description]);
    }
    @finally
    {
        NSLog(@"MP3生成成功: %@",mp3FilePath);
        [self loadData];
    }
}

- (NSDictionary *)audioRecordingSettings{
    
    NSDictionary *result = nil;
    
    NSMutableDictionary *recordSetting = [[NSMutableDictionary alloc]init];
    //设置录音格式  AVFormatIDKey==kAudioFormatLinearPCM
    [recordSetting setValue:[NSNumber numberWithInt:kAudioFormatLinearPCM] forKey:AVFormatIDKey];
//    [recordSetting setValue:[NSNumber numberWithInt:kAudioFormatAppleLossless] forKey:AVFormatIDKey];
    //设置录音采样率(Hz) 如：AVSampleRateKey==8000/44100/96000（影响音频的质量）
    [recordSetting setValue:[NSNumber numberWithFloat:11025.0] forKey:AVSampleRateKey];
    //录音通道数  1 或 2
    [recordSetting setValue:[NSNumber numberWithInt:2] forKey:AVNumberOfChannelsKey];
    //线性采样位数  8、16、24、32
//    [recordSetting setValue:[NSNumber numberWithInt:16] forKey:AVLinearPCMBitDepthKey];
    //录音的质量
    [recordSetting setValue:[NSNumber numberWithInt:AVAudioQualityHigh] forKey:AVEncoderAudioQualityKey];
    
    result = [NSDictionary dictionaryWithDictionary:recordSetting];
    return result;
}

- (NSString *)getAudioFilePath
{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
    return [paths[0] stringByAppendingPathComponent:@"asrview.wav"];
}

- (NSString *)getMp3FilePath
{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
    return [paths[0] stringByAppendingPathComponent:@"asrview.mp3"];
}

http://blog.csdn.net/ysy441088327/article/details/7392842
https://github.com/Superbil/build-lame-for-iOS