Data output apparatus that locks and unlocks data format

A method of controlling a data output apparatus having an output terminal, the method comprising:

• a first receiving step of receiving a first command from a first control device;
• a second receiving step of receiving a second command from a second control device different from the first control device;
• a setting step of setting the output terminal to a locked state where a data format of the output terminal is locked to a data format indicated by the first command and where the output terminal cannot output video data whose data format is different from the data format indicated by the first command, if the first command is received from the first control device while the output terminal is being set to an unlocked state where the data format of the output terminal is not locked to one data format;
• a determining step of determining whether a data format indicated by the second command is the same as the data format of the output terminal, if the second command is received from the second control device while the output terminal is being set to the locked state;
• and
• a transmitting step of transmitting a response for informing the second control device that the second command is accepted, if the data format indicated by the second command is the same as the data format of the output terminal, wherein the output terminal is an oPCR (output plug control register) defined by the IEC 61883-1 standard.