16. The sink device of claim 9 , wherein if the text converted from the re-received voice signal is not included in the recognized text, the controller is further configured to send the message corresponding to a user input on inputting the converted text through a keyboard input device to the source device through the network interface unit.
9. In controlling video data transmitted from a source device, a sink device comprising: an interface unit configured to communicate with the source device by Wi-Fi Direct; a receiving unit configured to receive a voice signal from a remote controller that is wirelessly connected to the sink device; a display unit; and a controller configured to: output the video data received from the source device through the network interface unit to the display unit, recognize a text from a screen corresponding to the video data outputted to the display unit, save the recognized text to a memory to correspond to location information on the screen corresponding to the video data, convert the voice signal received through the voice signal receiving unit into a text using a speech-to-text (STT) function at the sink device, and if a specific text including at least one portion of the converted text exists in the recognized text, send a message corresponding to a user input of selecting the specific text from the screen corresponding to the video data to the source device through the network interface unit via a user input back channel (UIBC), wherein the UIBC is not configured to transmit the voice signal.