在iPhone上使用LAME编码为.mp3时，如何显示进度条？

Question

我正在使用LAME在我的iPhone应用程序.caf音频文件编码为.mp3 。

一切工作正常，我正艰难地尝试弄清楚如何将音频文件转换的进度记录到.mp3 ，同时使用UIProgressView向用户显示进度。

我正在使用此代码（对Deepak Soni（ 可在此处获取 ）编写的原始代码进行了一些修改：

NSArray *dirPaths;
NSString *docsDir;

dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
docsDir = [dirPaths objectAtIndex:0];
_mp3FilePath = [docsDir stringByAppendingPathComponent:@"file.mp3"];

NSString* cafFile = [[NSBundle mainBundle] pathForResource:@"background" ofType:@"caf"];
char cstr[512] = {0};
[cafFile getCString:cstr maxLength:512 encoding:NSASCIIStringEncoding];


@try {
    int read, write;
    FILE *pcm = fopen([cafFile cStringUsingEncoding:1], "rb");
    FILE *mp3 = fopen([_mp3FilePath cStringUsingEncoding:1], "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, 44100);
    lame_set_VBR(lame, vbr_default);
    lame_init_params(lame);

    NSFileManager *fileManger = [NSFileManager defaultManager];
    NSData *data = [fileManger contentsAtPath:cafFile];
    NSString* str = [NSString stringWithFormat:@"%d K",[data length]/1024];
    NSLog(@"size of caf=%@",str);

    printf("Using LAME v%s\n", get_lame_version());

    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 {
    //Detrming the size of mp3 file
    NSFileManager *fileManger = [NSFileManager defaultManager];
    NSData *data = [fileManger contentsAtPath:_mp3FilePath];
    NSString* str = [NSString stringWithFormat:@"%d K",[data length]/1024];
    NSLog(@"size of mp3=%@",str);
}

Answer 1

我必须使用lame_set_num_samples ，然后lame_get_num_samples才能正常工作，如下所示：

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

    lame_t lame = lame_init();
    lame_set_in_samplerate(lame, 44100);
    lame_set_VBR(lame, vbr_default);
    lame_init_params(lame);

    NSString* cafFile = [[NSBundle mainBundle] pathForResource:@"background" ofType:@"caf"];
    char cstr[512] = {0};
    [cafFile getCString:cstr maxLength:512 encoding:NSASCIIStringEncoding];

    int fileSize = [[[NSFileManager defaultManager] attributesOfItemAtPath:cafFile error:nil] fileSize];
    int duration = (fileSize * 8) / (sampleRate * bitsPerSample * numberOfChannels);

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

    int percent     = 0;
    int samp_rate   = lame_get_out_samplerate(lame);
    int frameNum    = lame_get_frameNum(lame);
    int totalframes = lame_get_totalframes(lame);

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

    float progress = (float) percent/100;

    dispatch_async(dispatch_get_main_queue(), ^{

           self.percentageLabel.text = [NSString stringWithFormat:@"%d%%",percent];
           self.progressBar.progress =  progress;

        });