Image playback apparatus and playback method

When the recording format of an image recorded on a magnetic tape (709) is changed, a playback time period of an image signal by a REC review function is extended. Even when the recording format is changed during playback of an image signal by the REC review function, an image (409) recorded in the recording format after change can be displayed after a blue-backed screen (408) is displayed. Therefore, the user can determine whether the blue-backed screen (408) is displayed due to switching of the system or due to an unrecorded part of an image signal. Hence, the user can be prevented from overwriting a new image signal on the recorded region of an image signal by mistake.

FIELD OF THE INVENTION

The present invention relates to a playback apparatus, a playback method, and a computer program and, more particularly, to a technique suited to be used to play back image signals having different recording formats.

BACKGROUND OF THE INVENTION

Conventionally, a digital VTR which records an image signal on a magnetic tape as digital data is known. In recent years, a digital VTR which can record and play back a high-definition (HD) image in place of a conventional standard-definition (SD) image has been proposed (for example, see Japanese Patent Laid-Open No. 2001-275077). In such a digital VTR, a high-definition image signal obtained by photography is encoded by MPEG and is then recorded on a magnetic tape.

As the standard for consumer digital VTRs that record SD image signals, a DV format has been proposed. Furthermore, as the standard for consumer digital VTRs that record HD image signals, an HDV format (Hi-Vision format) has been proposed.

In this HDV format, the same magnetic tape as the DV format is used as a recording medium and an MPEG-encoded HD image signal is recorded and played back.

As a function of a video camera, a REC review function is known. In this function, after recording is paused, a tape is rewound by a predetermined amount, and playback is made up to the paused position.

As described above, the HDV format uses the same magnetic tape as in the DV format. Hence, a video camera which supports both the DV and HDV formats is available.

In such a video camera, an SD image signal recorded in the DV format and an HD image signal recorded in the HDV format can coexist on a single magnetic tape. For this reason, upon playback, the playback method of an image signal must be switched at a boundary between the recorded region in the DV format and that in the HDV format. As a result, output of a playback image may cease.

For example, when the boundary between the recorded region in the DV format and that in the HDV format is included in a zone to be played back by the aforementioned REC review function, the processing method must be switched at that boundary, and as a result an image ceases to be played back. Therefore, although an image signal is actually recorded on the magnetic tape, the user may misunderstand and believe that no signal is recorded.

As a result, when the user starts recording from the position where an image ceases to be played back, the originally recorded image may be overwritten and erased.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the above problems, and has as its object to prevent a new image signal from being inadvertently overwritten on a region where an image signal has already been recorded.

According to an aspect of the present invention, there is provided a playback apparatus comprising: playback adapted to play back image signals recorded in a plurality of different recording formats from a recording medium; recording review execution unit adapted to control, in response to issuance of a recording review instruction for an image signal recorded on the recording medium, the playback unit to rewind the recording medium from a position upon issuance of the recording review instruction by a predetermined amount and to play back the image signal from the recording medium for a period based on the predetermined amount from the rewound position; and detection unit adapted to detect a change in recording format of the image signal played back by the playback unit in accordance with the recording review instruction, wherein when the detection unit detects the change in recording format of the image signal, the recording review execution unit controls to execute a playback operation of the image signal for a longer period than the period based on the predetermined amount.

According to another aspect of the present invention, there is provided a playback method for playing back an image signal using playback unit adapted to play back image signals recorded in a plurality of different recording formats from a recording medium, comprising: a recording review execution step of controlling, in response to issuance of a recording review instruction for an image signal recorded on the recording medium, the playback unit to rewind the recording medium from a position upon issuance of the recording review instruction by a predetermined amount and to play back the image signal from the recording medium for a period based on the predetermined amount from the rewound position; and a detection step of detecting a change in recording format of the image signal played back by the playback unit in accordance with the recording review instruction, wherein the recording review execution step includes controlling, when the change in recording format of the image signal is detected in the detection step, to execute a playback operation of the image signal for a longer period than the period based on the predetermined amount.

According to a further aspect of the present invention, there is provided a computer program for making a computer execute a step of playing back an image signal using playback unit adapted to play back image signals recorded in a plurality of different recording formats from a recording medium, the program characterized by making the computer execute: a recording review execution step of controlling, in response to issuance of a recording review instruction for an image signal recorded on the recording medium, the playback unit to rewind the recording medium from a position upon issuance of the recording review instruction by a predetermined amount and to play back the image signal from the recording medium for a period based on the predetermined amount from the rewound position; and a detection step of detecting a change in recording format of the image signal played back by the playback unit in accordance with the recording review instruction, wherein the recording review execution step includes controlling, when the change in recording format of the image signal is detected in the detection step, to execute a playback operation of the image signal for a longer period than the period based on the predetermined amount.

With this arrangement, according to the present invention, a new image signal can be prevented from being overwritten on a recorded region of an image signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 1is a block diagram showing an example of the arrangement of a digital video camera (DVC) as an embodiment of a playback apparatus according to the present invention.

The video camera shown inFIG. 1can record and play back an SD image signal in the DV format and an HD image signal in the HDV format. The user can arbitrarily switch between the DV format and the HDV format upon recording by operating an operation unit712.

Referring toFIG. 1, an image sensing unit701is used to photograph an object, and outputs an SD or HD image signal. An input/output signal processor702applies known signal processing to the image signal output from the image sensing unit701, and outputs the image signal that has undergone the signal processing to a memory I/F707. Furthermore, the input/output signal processor702converts an image signal read out via the memory I/F707to a format suited to output in a playback mode.

An MPEG processor703encodes and decodes an HD image signal by MPEG. A DV processor704encodes and decodes an SD image signal according to an intra-frame encoding method specified in the DV format. A mux/demux unit705appends additional information including a sync signal and other data to image data output via the memory I/F707in a recording mode. Furthermore, the mux/demux unit705detects image data, additional information, and the like from data to be played back, and outputs them to the memory I/F707or a controller711in the playback mode.

A memory706is a large-capacity recording medium such as an SDRAM or the like. The memory I/F707controls read and write accesses of data between respective units and the memory706.

A recording/playback unit708records data in the DV or HDV format on a magnetic tape709. Furthermore, the recording/playback unit708plays back data in the DV or HDV format recorded on the magnetic tape709.

The controller711is used to control the processing of the digital video camera, and comprises, e.g., a CPU, ROM, and RAM. The ROM stores a program required to execute processing of this embodiment. The CPU executes the program stored in the ROM. The RAM serves as a work area used when the CPU executes the program stored in the ROM, and temporarily stores data.

The operation unit712has various switches such as a recording/playback trigger switch, REC review instruction switch, and the like. A tape transport mechanism713has a capstan motor, capstans, and the like, and transports the magnetic tape709. A display controller714generates data to be displayed on a display screen of a display unit715and outputs it to the display unit715in accordance with an image signal from the memory I/F707and an instruction from the controller711. The display unit715is, for example, a liquid crystal display device. An output unit716externally outputs playback image data.

Note that the image sensing unit701, input/output signal processor702, MPEG processor703, DV processor704, mux/demux unit705, recording/playback unit708, controller711, tape transport mechanism713, and display controller714are connected to a control bus710. These units can communicate with each other via the control bus710.

In the digital video camera shown inFIG. 1, the memory706is commonly used by the respective units, and read and write accesses to the memory706are arbitrated by the memory I/F707.

As described above, the user can select one of recording formats, i.e., the DV and HDV formats by operating the operation unit712upon recording. The controller711controls the memory I/F707in accordance with the recording format of user's choice to change address mapping on the memory706to a format suited to the recording format of user's choice.

When the user selects the DV format, the controller711controls the image sensing unit701to output an SD image. Also, the controller711controls the DV processor704to encode the sensed image. On the other hand, when the user selects the HDV format, the controller711controls the image sensing unit701to output an HD image. Also, the controller711controls the MPEG processor703to encode the photographed image.

In this manner, on the magnetic tape709as the recording medium, an image signal recorded in the DV format and that recorded in the HDV format can be mixed and recorded.

When the recorded image signal is read out from the magnetic tape709and is played back, the mux/demux unit705discriminates based on identification information in the readout signal if that signal was recorded in the DV or HDV format. The mux/demux unit705notifies the controller711of the discriminated recording format.

The controller711changes address mapping on the memory706according to the recording format notified by the mux/demux unit705. The controller711controls one of the MPEG processor703and DV processor704to decode the image signal according to the notified recording format. The controller711controls the display controller714to read out the decoded image signal via the memory I/F707, and to display it on the display unit715.

When the recording format of an image signal is changed during read-out of the image signal, the controller711controls the tape transport mechanism713to continue transporting of the magnetic tape709intact. Furthermore, the controller711controls the mux/demux unit705to stop a data write access to the memory I/F707. The controller711changes address mapping on the memory706via the memory I/F707. Upon completion of change of address mapping, the controller711controls the mux/demux unit705to restart the data write access to the memory I/F707.

A REC review function will be described below.

When the user operates a REC review switch of the operation unit712while he or she pauses the recording operation, the controller711controls the tape transport mechanism713to execute REC review processing as follows.

FIG. 2is a conceptual view showing information recorded on the magnetic tape709and an image to be displayed upon execution of the REC review function.

FIG. 2shows a case wherein data is recorded in only one recording format of the DV format and HDV format.

For example, when the user newly sets a magnetic tape709on which an image signal has already been recorded in the video camera, and is about to start recording, he or she may want to confirm if the recording start position poses no problem. In this case, the user can confirm if the current tape position poses no problem as the recording start position by using the REC review function at the current tape position.

When the REC review function is executed, the controller711controls the tape transport mechanism713to rewind the magnetic tape709from a tape stop position (full inverted-triangle mark inFIG. 2)102shown inFIG. 2by an amount corresponding to a predetermined time period. After that, the controller711controls the recording/playback unit708to play back an image signal recorded on the magnetic tape709for the predetermined time period (N seconds). The controller711then controls the display controller714to display a playback image103based on the played-back image signal on the display unit715. After that, when playback of the image signal to the tape stop position102ends, a standby state (recording paused state) is set.

The user confirms the recorded contents of the magnetic tape709by viewing the playback image103displayed on the display unit715and can determine if no problem is posed if he or she starts photography from the current position. If no problem is posed, the user inputs a photography start instruction to the digital video camera in the standby state, thus starting photography and recording.

That is, upon starting joint recording from a scene recorded at the tape stop position102of the magnetic tape709, the user confirms the recorded contents of the magnetic tape709using the aforementioned REC review function. Then, the user can determine if he or she can start recording from the current position of the magnetic tape709. Furthermore, by using the REC review function, the user can determine whether or not the magnetic tape709currently set in the digital video camera can be used in recording.

FIG. 3is a conceptual view showing an example of information recorded on the magnetic tape709and an image to be displayed upon execution of the REC review function.FIG. 3shows a case wherein an image recorded in the DV format and that recorded in the HDV format are mixed on the magnetic tape709.

Referring toFIG. 3, a region202(SD inFIG. 3) recorded in the DV format and a region203(HD inFIG. 3) recorded in the HDV format are mixed on the magnetic tape709.

Assume that a tape stop position205(full inverted-triangle mark inFIG. 3) is located within the region (DV format region)202recorded in the DV format. In this case, upon reception of an execution instruction of the REC review function, the controller711controls the tape transport mechanism713to rewind the magnetic tape709from the tape stop position205for a predetermined time period (N seconds). After that, the controller711controls the recording/playback unit708to play back an image signal recorded in the DV format for the predetermined time period (N seconds). The controller711then controls the display controller714to display a playback image207based on the played-back image signal on the display unit715.

Also, assume that a tape stop position206(open inverted-triangle mark inFIG. 3) is located within the region (HDV format region)203recorded in the HDV format. In this case, upon reception of an execution instruction of the REC review function, the controller711controls the tape transport mechanism713to rewind the magnetic tape709from the tape stop position205for a predetermined time period. After that, the controller711controls the recording/playback unit708to play back an image signal recorded in the HDV format for the predetermined time period (N seconds). The controller711then controls the display controller714to display a playback image208based on the played-back image signal on the display unit715.

Assume that the execution instruction of the REC review function is input when the tape stop position is located near a boundary204with the DV format region202within the HDV format region203. In this case, the controller711controls the recording/playback unit708to play back and display image signals recorded in both the DV format region202and HDV format region203from the magnetic tape709during single execution of the REC review function.

FIG. 4is a conceptual view showing an example of information recorded on the magnetic tape709and an image to be displayed upon execution of the REC review function. As inFIG. 3,FIG. 4shows a case wherein a DV format region302(SD inFIG. 4) and an HDV format region303(HD inFIG. 4) are mixed on the magnetic tape709. InFIG. 4, a tape stop position306is located near a boundary305with the DV format region302within the HDV format region303. A problem posed when the execution instruction of the REC review function is input in such situation will be described below with reference toFIG. 4.

When image signals recorded in different formats are to be played back, the internal processing of the digital video camera needs to be switched to a method suited to each individual recording format upon switching of the recording formats. However, this switching cannot be done instantly but it requires certain time.

Since a readout image signal cannot be normally processed during switching of the internal processing, for example, a blue-backed screen310may be displayed in place of an image on the display unit715, as shown inFIG. 4.

For example, assume that the execution instruction of the REC review function is input at the tape stop position306(full inverted-triangle mark inFIG. 4). In this case, the magnetic tape709is rewound from the tape stop position306for N seconds, and playback is started. Since the playback start position is located within the DV format region302, a playback image308by the internal processing corresponding to the DV format is displayed on the display unit715. When the recording format of the magnetic tape709is switched from the DV format to the HDV format from the boundary305, the internal processing must also be switched in correspondence with the HDV format.

The blue-backed screen310is displayed on the display unit715during switching of the internal processing. If switching is completed within the predetermined time period (N seconds) after the beginning of playback by the REC review function, an image signal309based on the image signal recorded in the HDV format can be displayed on the display unit715after display of the blue-backed screen310.

However, if switching of the internal processing is not completed before the end of playback by the REC review function, the playback operation of the image signal by the REC review function ends while the blue-backed screen310is displayed.

In general, when a region where no image signal is recorded is played back, a blue-backed screen is also displayed. For example, when a tape stop position (open inverted triangle mark inFIG. 4)307is located within an unrecorded region304of an image signal, if the execution instruction of the REC review function is input, a blue-backed screen311is displayed after an end position312of the HDV format region303.

In such situation, it is very difficult to discriminate whether the blue-backed screen is displayed due to the beginning of a region in the different recording format (blue-backed screen310) or due to the beginning of an unrecorded part of an image signal (blue-backed screen311).

As a result, the user may mistake the blue-backed screen310due to the beginning of the region in the different recording format for the blue-backed screen311due to the beginning of the “unrecorded part of an image signal”. When such misunderstanding occurs, the user may overwrite an image signal on the already recorded region (e.g., the HDV format region303inFIG. 3).

In order to avoid such situation, according to this embodiment, when a zone in which playback is made by the REC review function (to be referred to as a REC review zone hereinafter) includes a plurality of different format regions, the REC review operation is controlled as follows.

That is, When the REC review zone includes regions of different recording formats, the controller711changes a playback time period of an image signal by the REC review function. In other words, the controller711dynamically varies the REC review zone. More specifically, the controller711changes the playback time period so that the REC review function ends with display of an image in place of the blue-backed screen. With this control, the user can clearly identify the blue-backed screens310and311, and can be avoided from overwriting data on the already recorded region while mistaking for an unrecorded region.

FIG. 5is a conceptual view showing an example of information recorded on the magnetic tape709and an image to be displayed upon execution of the REC review function. As inFIG. 4,FIG. 5shows a case wherein a DV format region402(SD inFIG. 5), an HDV format region403(HD inFIG. 5), and an unrecorded region404of an image signal are mixed on the magnetic tape709.

FIG. 5shows an example of a method of solving the problem described usingFIG. 4.

As shown inFIG. 5, assume that, for example, a predetermined time period for playing back an image signal by executing the REC review function is set to be N seconds. When a change in recording format is detected during the REC review zone, the duration of the REC review zone is extended to (N+M) seconds.

Referring toFIG. 5, assume that the execution instruction of the REC review function is issued at a tape stop position406(full inverted-triangle mark inFIG. 5). In this case, the controller711controls the tape transport mechanism713to rewind the magnetic tape709from the tape stop position406for N seconds. The controller711then controls the recording/playback unit708to start playback. Since the playback start position is located within the DV format region402, the controller711controls the recording/playback unit708and DV processor704to display a playback image407based on the image signal recorded in the DV format on the display unit715.

When the playback image407based on the image signal recorded in the DV format is kept displayed on the display unit715, the position of the magnetic tape709moves to a boundary405between the regions402and403of different recording formats. Based on information from the mux/demux unit705, the controller711detects the beginning of the HDV format region403. The controller711changes the playback time period by the REC review function from N seconds to (N+M) seconds. That is, the controller711extends the REC review zone. At this time, the value M is set so that M seconds become longer than a time period required to switch from the DV format to the HDV format.

The controller711starts switching of the internal processing, and controls the display controller714to start display of a blue-backed screen408on the display unit715. Upon completion of switching, the controller711controls to start display of a playback image409based on the image signal in the HDV format region403and to stop the magnetic tape709after an elapse of (N+M) seconds from the beginning of playback. With this control, the user can view an image of the HDV format region403, and can recognize that the tape stop position406is not located within an unrecorded region.

As described above, according to this embodiment, the playback time period of an image signal by the REC review function is extended according to the recording format of an image recorded on the magnetic tape709. Even when the recording format is changed during playback of an image signal by the REC review function, the playback image409based on the signal recorded in the recording format after change can be displayed on the display unit715after the blue-backed screen408is displayed.

In this way, even when the boundary405between the regions recorded in different recording formats is located within the REC review zone, the contents recorded on the magnetic tape709can be displayed on the display unit715during REC review.

Since the image409recorded in the recording format after change can be displayed by extending the playback time period of an image signal by the REC review function, the REC review of the recorded region never ends with display of a blue-backed screen. For this reason, the user can determine whether a blue-backed screen is displayed owing to switching of the internal processing of the apparatus or owing to an unrecorded part of an image signal upon playing back an image signal by executing the REC review function. Therefore, the user can be avoided as much as possible from mistaking the blue-backed screen408displayed due to a change in recording format for a blue-backed screen displayed in correspondence with the unrecorded region404of an image signal on the magnetic tape709.

With the above control, the user can be prevented as much as possible from issuing a recording instruction of an image signal on an unintended recording region, and can be prevented as much as possible from overwriting a new image signal on the recorded region of an image signal by mistake.

In this embodiment, the magnetic tape709has been exemplified as a recording medium that records an image signal. However, the recording medium that records an image signal need not always be the magnetic tape709. For example, any other recording media such as a flexible disk and the like may be used as long as they perform recording.

Second Embodiment

The second embodiment of the present invention will be described below. This embodiment is substantially the same as the aforementioned first embodiment, except for some processes in the method of playing back an image signal upon execution of the REC review function. Therefore, in the following description, the same reference numerals as those inFIGS. 1 to 5denote the same parts as in the first embodiment, and a detailed description thereof will be omitted.

FIG. 6is a conceptual view showing an example of information recorded on the magnetic tape709and an image displayed upon execution of the REC review function.

As shown inFIG. 6, a tape stop position406(full inverted-triangle mark inFIG. 6) is located near a boundary405between a DV format region402and an HDV format region403. When the REC review function is executed in this state, image signals recorded in different recording formats are played back during single execution of the REC review function.

A playback image407based on the image signal recorded in the DV format is displayed on the display unit715, and the position of the magnetic tape709moves into the HDV format region403via the boundary405between the regions402and403of the different recording formats. After the mux/demux unit705detects the format of an image recorded in the HDV format, the controller711controls the recording/playback unit708to continue the playback operation of the image signal by the REC review function.

That is, after the internal processing of the digital video camera is changed from that for one format to support the other format, the controller711controls to continue the playback operation until the camera is ready to play back an image recorded in the other format. Then, the playback operation of the image signal by the REC review function ends when an image recorded in the other format can be played back, thus setting the standby state.

As described above, the playback operation of the image signal by the REC review function is continued until the digital video camera shifts from a playback state of an image recorded in the DV format to a state wherein it is ready to play back an image recorded in the HDV format.

Furthermore, the controller711executes the following processing during transition to the state the camera is ready to play back an image recorded in the HDV format by the REC review function, i.e., during switching of the internal processing of the digital video camera to support the HDV format. The controller711controls to display a blue-backed screen408on the display unit715, and to continuously execute the REC review function. After the internal processing of the digital video camera is switched to be able to support an image recorded in the HDV format, the controller711enables playback of an image signal by the continuously executed REC review function. In this way, a playback image509based on an image signal recorded in the HDV format can be displayed on the display unit715by the REC review function.

With the above control, the following effect can be obtained in addition to those described in the above-mentioned first embodiment. That is, the playback time period of an image signal by the REC review function can be changed in accordance with a time period required until the camera is ready to play back an image recorded in the HDV format.

Third Embodiment

The third embodiment of the present invention will be described below. This embodiment is substantially the same as the aforementioned first and second embodiments, except for an image displayed during switching (transition period) when switching of the internal processing occurs during execution of the REC review function. Therefore, in the following description, the same reference numerals as those inFIGS. 1 to 6denote the same parts as in the first and second embodiments, and a detailed description thereof will be omitted.

FIG. 7is a conceptual view showing an example of an image displayed upon execution of the REC review function.

As shown inFIG. 7, assume that the tape position moves into the HDV format region while a playback image407based on an image signal recorded in the DV format is displayed. As a result, the digital video camera begins to switch the internal processing to a state wherein it can display a playback image509based on an image signal recorded in the HDV format.

In the above embodiments, a blue-backed screen is displayed on the display unit715during this switching processing (transition period). By contrast, in this embodiment, an image that allows the user to recognize switching of the internal processing, e.g., a blue-backed screen608with text “SDHD” is displayed on the display unit715.

With this control, the user can determine at a glance whether a blue-backed screen is displayed due to the switching processing of the internal processing or due to an unrecorded part of an image signal.

Note that the contents attached to the blue-backed screen are not limited to those shown inFIG. 7. Text, a figure, or a symbol that allows the user to recognize mode transition, or a combination of them may be used. Alternatively, a different background color may be used.

Other Embodiments of the Present Invention

In the aforementioned embodiments, only the case has been explained wherein the recording format at the beginning of playback by the REC review function matches the internal processing method of the digital video camera. However, a case wherein they do not match may occur. In such case, since switching of the internal processing occurs at the beginning of playback, a blue-backed screen is displayed first. However, since the playback time period (N seconds) of the REC review function is normally longer than a time period required to switch the internal processing, the REC review function does not end with display of the blue-backed screen. Therefore, the playback time period of the REC review function need not be extended to cope with switching of the internal processing at the beginning of playback, and it need only be extended at the time of detection of a change in recording format within the REC review zone later.

Note that the blue-backed screen display described in the third embodiment can be made even during switching of the internal processing at the beginning of playback.

In the above embodiments, since the REC review zone (playback time period) is extended at the time of detection of a change in recording format within the REC review zone, the tape position upon completion of the REC review function is different from that upon reception of the execution instruction of the REC review function. For this reason, when the playback time period is extended, after playback by the REC review function ends, the magnetic tape may be rewound to the tape position upon reception of the execution instruction of the REC review function to set the standby state. Such embodiment can be easily implemented when the tape position upon reception of the execution instruction of the REC review function is stored, and the controller711controls the tape transport mechanism713to rewind the magnetic tape to the stored position.

The aforementioned embodiments can be implemented by software using a computer (or a CPU, MPU, or the like) of a system or an apparatus.

Therefore, a computer program itself supplied to the computer to implement the aforementioned embodiments by the computer also implements the present invention. That is, the computer program itself required to implement the functions of the aforementioned embodiments is one constituent element of the present invention.

Note that the form of the computer program required to implement the aforementioned embodiments is not particularly limited as long as the computer program is readable by the computer. For example, an object code, a program to be executed by an interpreter, script data to be supplied to an OS, and the like may be used, but the present invention is not limited to them.

The computer program required to implement the aforementioned embodiments is supplied to the computer via a storage medium or a wired/wireless communication. As the storage medium used to supply the program, for example, magnetic storage media such as a flexible disk, hard disk, magnetic tape, and the like, optical/magneto-optical storage media such as an MO, CD, DVD, and the like, a nonvolatile semiconductor memory, and the like may be used.

As the supply method of the computer program using the wired/wireless communication, a method utilizing a server on a computer network is available. In this case, a data file (program file) which can be the computer program that forms the present invention is stored in the server. As the program file, a file having an executable format, source codes, and the like may be used.

The program file is supplied to a client computer which accesses this server by downloading the program file. In this case, the program file may be divided into a plurality of segment files, which may be distributed and allocated in different servers.

That is, the server which provides the program file required to implement the aforementioned embodiments to the client computer is one of the present invention.

A storage medium that stores the encrypted computer program required to implement the aforementioned embodiments may be delivered to the user, and the user who has cleared a predetermined condition may be allowed to receive key information used to decrypt the encrypted program and to install the decrypted program in his or her computer. The key information can be supplied by downloading it from a homepage via, e.g., the Internet.

The computer program required to implement the aforementioned embodiments may utilize the functions of an OS which is already running on the computer.

Furthermore, some functions of the computer program required to implement the aforementioned embodiments may be configured by firmware in an expansion board or the like connected to the computer, or the computer program may be executed by a CPU of the expansion board or the like.

This application claims the benefit of Japanese Patent Application No. 2005-212744 filed on Jul. 22, 2005, which is hereby incorporated by reference herein its entirety.