iOS 使用lamemp3库将PCM录音数据压缩为MP3格式

根据pcm文件转MP3

• (void)conventToMp3 {
  NSString *cafFilePath = [NSTemporaryDirectory() stringByAppendingString:@"VoiceInputFile"];
  self.mp3FilePath = [[NSUUID UUID] UUIDString];
  self.mp3FilePath = [self.mp3FilePath stringByAppendingString:@".mp3"];
  NSString *mp3FilePath = [[NSHomeDirectory() stringByAppendingFormat:@"/Documents/"] stringByAppendingPathComponent:self.mp3FilePath];

  @try {

    int read, write;
    
    FILE *pcm = fopen([cafFilePath cStringUsingEncoding:NSASCIIStringEncoding], "rb");
    FILE *mp3 = fopen([mp3FilePath cStringUsingEncoding:NSASCIIStringEncoding], "wb");
    
    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, self.sampleRate);
    lame_set_VBR(lame, vbr_default);
    lame_init_params(lame);
    
    long curpos;
    BOOL isSkipPCMHeader = NO;
    
    do {
        
        curpos = ftell(pcm);
        
        long startPos = ftell(pcm);
        
        fseek(pcm, 0, SEEK_END);
        long endPos = ftell(pcm);
        
        long length = endPos - startPos;
        
        fseek(pcm, curpos, SEEK_SET);
        
        
        if (length > PCM_SIZE * 2 * sizeof(short int)) {
            
            if (!isSkipPCMHeader) {
                //Uump audio file header, If you do not skip file header
                //you will heard some noise at the beginning!!!
                fseek(pcm, 4 * 1024, SEEK_SET);
                isSkipPCMHeader = YES;
            }
            
            read = (int)fread(pcm_buffer, 2 * sizeof(short int), PCM_SIZE, pcm);
            write = lame_encode_buffer_interleaved(lame, pcm_buffer, read, mp3_buffer, MP3_SIZE);
            fwrite(mp3_buffer, write, 1, mp3);
        }
        
        else {
            
            [NSThread sleepForTimeInterval:0.05];
        }
        
    } while (!self.isStopRecorde);
    
    read = (int)fread(pcm_buffer, 2 * sizeof(short int), PCM_SIZE, pcm);
    write = lame_encode_flush(lame, mp3_buffer, MP3_SIZE);
    lame_close(lame);
    fclose(mp3);
    fclose(pcm);
    
    self.isFinishConvert = YES;
  

  }
  @catch (NSException *exception) {

  }
  @finally {

  }
  }

参数设置
/** mp3压缩参数 /
_lame = lame_init();
/* 单声道 /
lame_set_num_channels(_lame, 1);
/* 16K采样率 决定 音质 清晰度 /
lame_set_in_samplerate(_lame, 16000);
lame_set_out_samplerate(_lame, 16000);
/* 压缩的比特率为16K 决定mp3 文件大小 */
lame_set_brate(_lame, 16);
仔细阅读以下博客 你会有所收获

实时格式化pcm --> mp3

http://code4app.com/forum.php?mod=viewthread&tid=6211

http://www.cnblogs.com/ios8/p/IOS-PCM-MP3.html

边录边转详解

http://ikinglai.blog.51cto.com/6220785/1228309