In recent years, mainly in the field of consumer video/sound equipment, general practice has been to connect an output apparatus such as a DVD player to a receiving apparatus such as a display via a network, and to view content, which is reproduced and outputted by the output apparatus, on the output apparatus.
As an interface standard for transmitting digital video and audio signals between the output apparatus and the receiving apparatus, a standard called “High-Definition. Multimedia Interface” (hereinafter, referred to as the “HDMI”; see Non-Patent Document 1) is established.
Because the HDMI standard makes it possible to transmit video and audio data in high-quality and uncompressed form, and the audio data is transmitted along with a video signal with a blanking period in which the audio data is superimposed (hereinafter, such a signal is referred to as the “HDMI signal”), the HDMI standard has advantages, for example, in that it is not necessary to separate an audio output terminal and a video output terminal as is required conventionally. Furthermore, the standard is expected to come into wide use in the future because the HDMI signal being transferred is encoded and thus copyright-protected.
In the HDMI, basically, a plurality of apparatuses are connected in series via cables conforming to the HDMI standard (hereinafter, referred to as the “HDMI cables”), and signals are transmitted between the apparatuses in one direction. The apparatuses are classified into three types:                (1) “Source” for transmitting signals (hereinafter, referred to as the “source apparatus”);        (2) “Sink” for receiving signals (hereinafter, referred to as the “sink apparatus”); and        (3) “Repeater” disposed between the source apparatus and the sink apparatus and having abilities to receive and retransmit signals as well as, for example, a 1-input/1-output or multi input/multi output selector function for selecting the source apparatus or the sink apparatus (hereinafter, referred to as the “repeater apparatus”).        
Note that the repeater apparatus does not simply pass the signals therethrough, but has in itself abilities both as the sink apparatus and as the source apparatus, and functions for reproducing a video signal and an audio signal by decoding a received HDMI signal, and reconverting these signals into an HDMI signal before retransmission.
The repeater apparatus is not only used as a selector, but also can be used as one of the apparatuses for constructing a home theater system in which, for example, the repeater apparatus itself has an audio reproduction and output ability, allowing the repeater apparatus to output an audio signal, which is received from a source apparatus such as a DVD player, from its own audio reproduction equipment, and retransmit a video signal to a sink apparatus for displaying the signal on a display.
Note that the sink apparatus at least stores information called “Extended Display Identification Data” (hereinafter, referred to as the “EDID”; see Non-Patent Document 2) for defining formats of video and audio signals, and the source apparatus can reference the EDID information in the sink apparatus by reading it via a serial signal line called a “DDC” in the HDMI cable.
The EDID information is information concerning formats of video and audio signals that can be reproduced after being received by the sink apparatus. By using the EDID information, the source apparatus can transmit a signal after automatically determining an optimal format of the signal in accordance with the sink apparatus connected thereto.
For example, when the EDID information indicates THAT “THE FORMAT OF THE VIDEO SIGNAL IS COMPATIBLE WITH 480P and 1080i, and the format of the audio signal is a linear PCM 2-channel format and compatible with sampling frequencies of up to 192 kHz”, the source apparatus can operate in such a manner as “not to use 720p but to output audio of up to 192 kHz without limiting the audio at 48 kHz”.
Accordingly, in order to ensure the aforementioned mechanism, the repeater apparatus is required to perform control in such a manner that the EDID information in the sink apparatus connected thereto can be referenced by the source apparatus as EDID information of the repeater apparatus itself.
Note that 480p, 1080i, and 720p as mentioned above denote video signal display formats, where numerals denote the number of scanning lines, p denotes progressive scanning mode, and i denotes interlaced scanning mode.    Non-Patent Document 1: “High-Definition Multimedia Interface Specification Version 1.1”, 2004    Non-Patent Document 2: “ENHANCED EXTENDED DISPLAY IDENTIFICATION DATA STANDARD Release A, Revision 1 VESA,”, 2002
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