1. Field of the Invention
This invention relates to a videophone that is capable of storing video signals and sound signals.
2. Description of the Related Art
In recent years, a technique of compressing information content has been largely advanced and a high-speed digital line has been becoming popular. This facilitates development of videophones that intercommunicate sound signals and video signals (dynamic image) at the same time. For example, such a videophone is shown in pages 35 to 42 of "International Standards of Video Conference System", that is described in the December issue of 1990 of "Communication Technology" published by Rick Telocom Co. Ltd. The videophone makes it possible to talk while seeing an image of a party.
However, the above device does not to automatically store video signals from one party in response to call signals of a telephone, when the other party is out, for example. Therefore, it is impossible with this device to confirm pictures after coming home, in case a call occurs while a called party is absent.
Then, there has been proposed a device that automatically stores the video signals of the transmitting party together with the sound signals or a storage start time, in response to the call signals at the time of absense (refer to Japanese Laid Open Patent Publication No. 2-119491).
However, with respect to automatically answering a phone call when the party is not at home, the above conventional device starts storing video signals and sound signals simultaneously with ending of transmission of a voice message that informs a caller of the absence of a called party. As such, a transmitting side (calling party) cannot start storing pictures and speeches at his or her intention, i.e. whenever desired.
This is because there is no system for sending a request to start storing from the transmitting side videophone to the receiving side (called side) videophone. Another reason is that, in case the called side receives the video signals processed by a previous-sample difference coding method which can lessen information amount, it is impossible to decode and play back the signals if the signals are stored halfway. Here, the previous-sample difference coding method is a coding method that encodes one frame of video signals in beginning communication and, thereafter, encodes only the changed part of the image, i.e. only the differences.
There may be proposed one method in which a receiving side videophone decodes and stores the received video signals, as a technique to solve the latter problem.