'Guess if frames are constant bit rate. If it returns False, you can
be sure that frames are variable bit rate. Otherwise, it looks like
constant bit rate (on first count fields).'

def looksConstantBitRate(self, count=10):

    check_keys = ('version', 'layer', 'bit_rate')
    last_field = None
    for (index, field) in enumerate(self.array('frame')):
        if last_field:
            for key in check_keys:
                if (field[key].value != last_field[key].value):
                    return False
        last_field = field
        if (index == count):
            break
    return True
