ios - Lame - 将比特率增加到 320

Question

首先我想展示一下我通过 Lame 库将源 .wav 文件转换为 .mp3 的方法:

- (void)convertFromWav:(NSString *)sourceFilePath ToMp3:(NSString *)resultName {
  NSString *mp3FileName = [resultName stringByAppendingString:@".mp3"];
  NSString *mp3FilePath = [NSTemporaryDirectory() stringByAppendingPathComponent:mp3FileName];

  @try {
    int read, write;
    FILE *pcm = fopen([sourceFilePath UTF8String], "rb");  //source
    if (pcm == NULL) {
      perror("fopen");
      return;
    }
    fseek(pcm, 4*1024, SEEK_CUR);                                   //skip file header
    FILE *mp3 = fopen([mp3FilePath cStringUsingEncoding:1], "wb");  //output

    const int sampleRate = 44100;
    const int bitsPerSample = 16;
    const int numberOfChannels = 2;

    const int PCM_SIZE = 8192*2;
    const int MP3_SIZE = 8192*2;
    short int pcm_buffer[PCM_SIZE*2];
    unsigned char mp3_buffer[MP3_SIZE];

    lame_t lame = lame_init();
    lame_set_in_samplerate(lame, sampleRate);
    lame_set_VBR(lame, vbr_default);
    lame_init_params(lame);

    lame_get_num_samples(lame);

    long long fileSize = [[[[NSFileManager defaultManager] attributesOfItemAtPath:sourceFilePath error:nil] objectForKey:NSFileSize] longLongValue];
    long duration = fileSize / (sampleRate * numberOfChannels * bitsPerSample / 8);//(fileSize * 8.0f) / (sampleRate * 2);

    lame_set_num_samples(lame, (duration * sampleRate));
    lame_get_num_samples(lame);

    float percent     = 0.0;
    int totalframes = lame_get_totalframes(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);

      int frameNum    = lame_get_frameNum(lame);
      if (frameNum < totalframes)
        percent = (100. * frameNum / totalframes + 0.5);
      else
        percent = 100;

      if ([_delegate respondsToSelector:@selector(convertingProgressChangedWithPercent:)])
      {
        [_delegate convertingProgressChangedWithPercent:percent];
      }

    } while (read != 0);

    lame_close(lame);
    fclose(mp3);
    fclose(pcm);
  }
  @catch (NSException *exception) {
    NSLog(@"%@",[exception description]);
  }
  @finally {
    if ([_delegate respondsToSelector:@selector(convertingDidFinish:)])
    {
      [_delegate convertingDidFinish:mp3FilePath];
    }
  }
}

没关系，它正在工作。结果我得到了每秒 152000 位的 .mp3。但我想让它达到每秒 320000 位。我该如何改变它？我对这些东西的理论并不擅长，所以我不知道哪些值会改变什么。谢谢。

Answer 1

您想使用 lame_set_VBR (lame_t, vbr_off); 然后您可以使用 lame_set_brate 来设置所需的比特率。使用 vbr_off 为您提供 CBR 模式，正如文档中所确认的那样(参见 headers.h ):

*********************************************************************
VBR control
************************************************************************
/* Types of VBR. default = vbr_off = CBR */
int CDECL lame_set_VBR(lame_global_flags *, vbr_mode);
vbr_mode CDECL lame_get_VBR(const lame_global_flags *);

试试这个:

//# for constants of settings
const int sampleRate = 44100;
const int bitsPerSample = 16;
const int numberOfChannels = 2;

const int myBitRate = 320;

//# for Lame settings
lame_t lame = lame_init();
lame_set_in_samplerate  (lame_t, sampleRate); //is 44100
lame_set_VBR            (lame_t, vbr_off); //force CBR mode
lame_set_brate          (lame_t, myBitRate); //is 320
lame_init_params        (lame_t);

你也可以像这样设置 Lame :
lame_t lame = lame_init(); 变成这样:lame_t = lame_init();

只是说，如果您定义了一个 lame_t，我希望它在其余设置中需要该名称。你知道像 lame_init_params (lame_t); 等