问题描述

转码mp3格式时显示进度条。

使用 LAME 将.caf音频文件编码为.mp3文件。

只有一个问题，需要计算转换文件的时间，用UIProgressView给用户显示转换进度，这点实现不了。

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%sn", 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);
}

解决方案

我建议使用lame_set_num_samples ，像这样：

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;

    });