'Graphics Control Extension. A sort of header at the start of
each image. Specifies transparancy and duration.'

def _get_graphics_control_ext(self, duration=0.1):

    bb = '!\xf9\x04'
    bb += '\x08'
    bb += int_to_bin(int((duration * 100)))
    bb += '\x00'
    bb += '\x00'
    return bb
