anchor.diff:          0 | // 7   user input - 0 = none
           transparency); // 8   transparency flag
   
  -    output.writeUint16(delay); // delay x 1/100 sec
  +    output.writeUint16(_lastImageDuration ?? delay); // delay x 1/100 sec
       output.writeByte(0); // transparent color index
       output.writeByte(0); // block terminator
     }
  
positive.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 (duration != null) {
        delay = duration;
      }
  
      if (output == null) {
        output = OutputBuffer();
  
        _lastColorMap = NeuralQuantizer(image, samplingFactor: samplingFactor);
        _lastImage = _lastColorMap.getIndexMap(image);
  
        _width = image.width;
        _height = image.height;
  
negative.code: 
      _lastColorMap = NeuralQuantizer(image, samplingFactor: samplingFactor);
      _lastImage = _lastColorMap.getIndexMap(image);
      _lastImageDuration = duration;
    }
  
    /// Encode the images that were added with [addFrame].
  