def create_stream(data_type, transaction_id):
    """
    Construct a 'createStream' message to issue a new stream on which data can travel through.
    :param data_type: int the RTMP datatype.
    :param transaction_id: int the transaction id in which the message will be sent on.
    """
    msg = {'msg': data_type,
           'command': [u'createStream', transaction_id, None]}
    return msg