def save
      pos = @io.pos
      @io.pos = @start_at
      @io << [Filter.guess(@filter_type)].pack('C')
      @io << self.data.slice(0, @data_size).ljust(@data_size, "\0")
      @io.pos = pos
      @callback.call(self) unless @callback.nil?
      self
    end
def save
      pos = @io.pos
      @io.pos = @start_at
      @io << [Filter.guess(@filter_type)].pack('C')
      @io << self.data.slice(0, @data_size).ljust(@data_size, "\0")
      @io.pos = pos
      @callback.call(self) unless @callback.nil?
      self
    end
Save the changes.