A sink device for controlling video data transmitted from a source device, the sink device comprising: a network interface unit configured to communicate with the source device by Wi-Fi Direct; a voice signal receiving unit configured to receive a voice signal; a storage unit; 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 the video data outputted to the display unit; save screen coordinates information of the recognized text to the storage unit; convert a user input voice signal received through the voice signal receiving unit into a text; and if a specific text, including at least one portion of the converted text, exists among texts corresponding to commands transmittable through user input back channel, UIBC, which are stored in the storage unit, send a message which includes at least a transmittable command corresponding to the user input and which includes information regarding selecting screen information corresponding to the previously saved screen coordinates of the recognized text from a screen corresponding to the video data to the source device through the network interface unit, wherein a prescribed function is executed on the source device in response to receiving the message from the sink device. a network interface unit configured to communicate with the source device by Wi-Fi Direct; a voice signal receiving unit configured to receive a voice signal; a storage unit; 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 the video data outputted to the display unit; save screen coordinates information of the recognized text to the storage unit; convert a user input voice signal received through the voice signal receiving unit into a text; and if a specific text, including at least one portion of the converted text, exists among texts corresponding to commands transmittable through user input back channel, UIBC, which are stored in the storage unit, send a message which includes at least a transmittable command corresponding to the user input and which includes information regarding selecting screen information corresponding to the previously saved screen coordinates of the recognized text from a screen corresponding to the video data to the source device through the network interface unit, output the video data received from the source device through the network interface unit to the display unit; recognize a text from the video data outputted to the display unit; save screen coordinates information of the recognized text to the storage unit; convert a user input voice signal received through the voice signal receiving unit into a text; and if a specific text, including at least one portion of the converted text, exists among texts corresponding to commands transmittable through user input back channel, UIBC, which are stored in the storage unit, send a message which includes at least a transmittable command corresponding to the user input and which includes information regarding selecting screen information corresponding to the previously saved screen coordinates of the recognized text from a screen corresponding to the video data to the source device through the network interface unit, wherein a prescribed function is executed on the source device in response to receiving the message from the sink device.