Method and apparatus for monitoring TV channel selecting status

An apparatus for monitoring the channel selecting status of a TV set which has a plurality of video/audio sources built-in and at least one video/audio input terminal for inputting video and audio signals from at least one external video/audio source, said TV set being capable of providing a display and an acoustic output of the video and audio signals supplied from a user's arbitrarily selected one of said video/audio sources, said apparatus comprising:

• sync signal detecting means for detecting vertical and horizontal sync signals of a video signal applied to a cathode-ray tube of said TV set;
• internal video signal detecting means for detecting video signals output from said plurality of video/audio sources built in said TV set;
• external video signal detecting means for detecting a video signal output from said video/audio source connected to said video/audio input terminal of said TV set;
• an analog switch which is supplied with said video signals detected by said internal video signal detecting means and said video signal detected by said external video signal detecting means, and selectively outputs one of said video signals;
• first sync separating means for separating vertical and horizontal sync signals from said video signal output from said analog switch;
• time difference measuring means which is supplied with first and second vertical and horizontal sync signals, and measures the time differences between said first and second vertical sync signals and between said first and second horizontal sync signals;
• control means which:
• inputs said vertical and horizontal sync signals detected by said sync signal detecting means, as said first vertical and horizontal sync signals, to said time difference measuring means;
• inputs said vertical and horizontal sync signals separated by said first sync separating means from said video signal of each of said video/audio sources selectively fed thereto from said analog switch, as said second vertical and horizontal sync signals, to said time difference measuring means;
• measures, by said time difference measuring means, the time differences between said vertical and horizontal sync signals detected by said sync signal detecting means and said vertical and horizontal sync signals of said each video/audio source;
• corrects said measured time differences in accordance with a premeasured delay time inherent in said each video/audio source;
• and determines that one of said video/audio sources for which said corrected time difference is minimum is the video/audio source currently selected by said user;
• a plurality of reference receivers for generating video signals of each channel of each TV broadcast independently of said TV set;
• second sync separating means for separating vertical and horizontal sync signals from each of said video signals generated by said reference receivers;
• and
• a selector for selectively outputting either said vertical and horizontal sync signals detected by said sync signal detecting means or said vertical and horizontal sync signals separated by said second sync separating means;
• wherein said control means:
• inputs a video signal of said that one of video/audio source determined as being currently selected by said user, to said first sync separating means via said analog switch inputs vertical and horizontal sync signals separated by said first sync separating means, as said first vertical and horizontal sync signals, to said time difference measuring means;
• sequentially generates, by said reference receivers, video signals of respective channels receivable from that one of said video/audio sources determined as currently selected by said user, and applies said video signals to said second sync separating means one by one;
• inputs vertical and horizontal sync signals separated by said second sync separating means, as said second vertical and horizontal sync signals, to said time difference measuring means;
• measures, by said time difference measuring means, the time differences between vertical and horizontal sync signals output from that one of said video/audio sources determined as currently selected by said user and vertical and horizontal sync signals of each channel generated by said reference receivers;
• corrects said measured time differences in accordance with a premeasured delay time inherent in said each of said plurality of video/audio sources;
• and determines that a channel for which said corrected time difference is smaller than a predetermined threshold value is a candidate for a channel currently selected by said user.