anchor.diff:  
       _lastColorMap = NeuralQuantizer(image, samplingFactor: samplingFactor);
       _lastImage = _lastColorMap.getIndexMap(image);
  +    _lastImageDuration = duration;
     }
   
     /// Encode the images that were added with [addFrame].
  
positive.code:         0 | // 7   user input - 0 = none
          transparency); // 8   transparency flag
  
      output.writeUint16(delay); // delay x 1/100 sec
      output.writeByte(0); // transparent color index
      output.writeByte(0); // block terminator
    }
  
negative.code:   /// After the last frame has been added, [finish] is required to be called.
    /// Optional frame [duration] is in 1/100 sec.
    void addFrame(Image image, {int duration}) {
      if (output == null) {
        output = OutputBuffer();
  
        _lastColorMap = NeuralQuantizer(image, samplingFactor: samplingFactor);
        _lastImage = _lastColorMap.getIndexMap(image);
        _lastImageDuration = duration;
  
        _width = image.width;
        _height = image.height;
  