Parsing duration of VBR audio is painfully slow

[leetreveil]

Parsing duration of VBR audio is painfully slow

[Pheo-Player]

As far as I can see, this is because musicmetadata does not try to read Xing headers, and always waits for all frames to be counted for a duration calculation (which is what you should do, when you get a file with no Xing headers). See here (id3v2.js, l. 133-142):

// once we know the file is VBR attach listener to end of
// stream so we can do the duration calculation when we
// have counted all the frames
if (readDuration && frameCount === 4) {
  stream.once('end', function () {
    callback('duration', calcDuration(frameCount,
      header.samples_per_frame, header.sample_rate))
    done()
  })
}

taglib, on the other hand, does this. It seems to implement a fairly simple class for these headers (xingheader.cpp, l. 91-115):

void MPEG::XingHeader::parse(const ByteVector &data)
{
  // Check to see if a valid Xing header is available.

  if(!data.startsWith("Xing") && !data.startsWith("Info"))
    return;

  // If the XingHeader doesn't contain the number of frames and the total stream
  // info it's invalid.

  if(!(data[7] & 0x01)) {
    debug("MPEG::XingHeader::parse() -- Xing header doesn't contain the total number of frames.");
    return;
  }

  if(!(data[7] & 0x02)) {
    debug("MPEG::XingHeader::parse() -- Xing header doesn't contain the total stream size.");
    return;
  }

  d->frames = data.toUInt(8U); // publicly accessible as totalFrames()
  d->size   = data.toUInt(12U); // publicly accessible as totalSize()

  d->valid = true; // publicly accessible as isValid()
}

which is used like this (mpegproperties.cpp, l. 212-225):

// Read the length and the bitrate from the Xing header.

if(d->xingHeader->isValid() &&
   firstHeader.sampleRate() > 0 &&
   d->xingHeader->totalFrames() > 0)
{
    double timePerFrame =
      double(firstHeader.samplesPerFrame()) / firstHeader.sampleRate();

    double length = timePerFrame * d->xingHeader->totalFrames();

    d->length = int(length);
    d->bitrate = d->length > 0 ? (int)(d->xingHeader->totalSize() * 8 / length / 1000) : 0;
}

This doesn't look too hard to implement to me, but I haven't read deep into this library's code and don't feel capable of doing this.

The following might be helpful too: http://www.codeproject.com/Articles/8295/MPEG-Audio-Frame-Header#XINGHeader

[leetreveil]

Closing this now, feel free to reopen if this is still an issue for you.