JP2000115745A - Video on-demand system and method for serving the video on-demand service - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the need for provision of a decoder to each client in the case that a vide on-demand VOD service is served with a video server using an existing CATV network. SOLUTION: A video server 20 transmits compressed digital video data having been stored in advance to a digital network 21 via a network interface 201 while keeping the video data compressed in response to a request from a client connecting to a CATV network 11. On the other hand, the compressed digital video data transmitted via the network 21 are received by a repeater 22 placed between the CATV network 11 and the network 21 and a decoder in the repeater 22 decodes the data and a modulator in the repeater 22 modulates the decoded data in a way that the data can be received by the client (set top box STB 12) and the modulated data are transmitted to the CATV network 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MPEG (Moving Picture Experts Group) stored in a video server.
A video-on-demand system and a video-on-demand service providing method for transmitting video data compressed by p) or the like to a client connected to a CATV (cable television) network via a network in response to a request from the client About.

[0002]

2. Description of the Related Art A video server includes a hard disk in a data format in which video data (here, video data including audio data, ie, all video / audio data are collectively represented as video data) is compressed by MPEG. Are stored in storage media such as
The data is also transmitted to the client in the compressed data format. This is to use storage media and networks efficiently.

[0003] Compressed digital video data transmitted from a video server to a network is received by a set-top box (hereinafter referred to as STB) connected to a display device (capable of outputting audio) on the client side. . The STB has a built-in decoder, decodes the received data, and reproduces the original data. The data decoded by the STB is displayed and output by the display device.

A network connecting the video server and each STB includes a digital network using a normal LAN (local area network) or WAN (wide area network), an existing CATV network and a CCTV network (hereinafter, these two networks). Are collectively referred to as a CATV network). Although modulation and demodulation are performed according to the network format, the data received by the STB is in a compressed data format.

FIG. 9 shows a configuration example of an existing system (CATV service system) using a CATV network. The video transmission device 90 multiplex-modulates an uncompressed video signal by the modulator 901 and transmits the multiplexed signal to the CATV network 91. Video signals are treated as analog signals. In an existing CATV service system, a video such as a movie to be transmitted is transmitted according to a predetermined program table, so that data other than a program currently being broadcast need not necessarily be in a transmittable state. Therefore, the video signal does not need to be recorded in a compressed form.

The CATV network 91 is for distributing multiplexed video signals, and usually uses a coaxial cable. This CATV network 91 has an STB on the client side.
92 are connected. The STB 92 is a CATV network 91
From the multiplexed video signal transmitted through the CDMA, a dedicated demodulator 921 extracts only the channel requested by the client, and performs a demodulation process to obtain a normal video signal via the cable 93 (television receiver). And the like).

Next, FIG. 10 shows a configuration example of a conventional video-on-demand (hereinafter, referred to as VOD) system using an existing CATV network. The same parts as those in FIG. 9 are denoted by the same reference numerals.

In the VOD system, unlike the CATV service system, the video to be transmitted is determined by a client request. Therefore, the video server 900 corresponding to the video transmission device 90 in FIG. 9 needs to accumulate video data (video / audio data) in such a manner that the video data can always be transmitted. So video server 9
00 is H in the form of video data compressed by MPEG or the like.
The data is stored in a storage medium such as a DD (hard disk) or a DVD (digital video disk), and is read from the storage medium in response to a client request. In an actual VOD system, a network or a mechanism for performing communication such as notifying a request from a client to a server is required, but is omitted here.

The video server 900 uses a modulator 910 having an analog conversion / multiplexing function to transmit the compressed video data (digital data) read from the storage medium to the CATV network 91 (an analog network). Convert to analog and multiplex. As described above, the video server 900 transmits the compressed video data as it is on the CATV network 91 without decoding the video data in order to perform efficient data transfer.

In the STB 920 on the client side, CA
Upon receiving the video data (data converted into analog) transmitted via the TV network 91, a built-in demodulator 92
In step 2, a process is performed to return to digital data and extract data of a necessary channel. The video data extracted by the demodulator 922 is sent to a decoder 923 in the same STB 920. The decoder 923 decodes the data (compressed data) sent from the demodulator 922 and transmits it as a normal video signal to the display device 94 via the cable 93.

[0011]

As described above, VO
The video server in the D system handles video data in a compressed format in order to efficiently store and transmit the data. Therefore, it is necessary to decode the compressed data on the STB side. That is, a decoder is required on the STB side. On the other hand, in the CATV service, there is no need to handle video data in a compressed format, so that a decoder is not required on the STB side.

The compressed data applied in the VOD system is digital data. Therefore, when an existing CATV network (a coaxial cable thereof) is used as a network used for video data distribution, QAM (Quadra
multiplex modulation and DA
(Digital / Analog) / AD (Analog / Digital)
The conversion must be performed at the gateway of the CATV network.

That is, in the VOD system, the existing C
When trying to use the ATV network, unlike the CATV service, there is a problem that a decoder is required for each client (STB on the side).

The present invention has been made in view of the above circumstances. An object of the present invention is to provide a VOD service by a video server using an existing CATV network without having to prepare a decoder for each client. It is to provide a VOD system and a VOD service providing method.

[0015]

SUMMARY OF THE INVENTION According to the present invention, there is provided a video transmission system in which compressed digital video data stored in advance is transmitted through a network interface while being compressed in response to a request from a client connected to a CATV network. A digital network provided for transmitting compressed digital video data transmitted from the video server; and a compressed digital video transmitted between the digital network and the CATV network and transmitted via the digital network. A decoder for decoding data, and a video data decoded by the decoder, which is modulated so as to be receivable on the client side and CAT
And a relay device having a modulator for transmitting to the V network.

As described above, the relay device having a built-in decoder is arranged between the video server and the client, specifically, between the digital network to which the video server is connected and the CATV network on the client side. On the digital network that connects them, video data requested from the client side is transferred in a compressed form, that is, as compressed digital video data, and the data is transferred by a decoder (in the relay device) at a relay point. By decoding, modulating with a modulator, and transmitting to a CATV network, unlike a conventional VOD service using a CATV network as shown in FIG. 10, there is no need to have a decoder for each client, In addition, the STB and cable network for CATV can be used as they are, and VOD It is possible to provide a service.

Further, since the compressed video data is transferred between the video server and the decoder, it is possible to efficiently transmit data from the video server without deteriorating the image quality (image quality). Further, since the distance between the decoder and the client can be reduced,
It is also possible to prevent the image quality from deteriorating due to the transmission of the decoder output over the CATV network.

Here, if the client is an apartment house in a remote area, and if the above-described configuration in which the relay device having the decoder and the modulator is arranged for each apartment house, that is, for each predetermined unit, is applied. And the actual distance of transmission on the CATV network can be further reduced, and deterioration of image quality can be suppressed efficiently.

Further, the present invention is characterized in that the decoder is configured such that an output image can be changed according to a control signal from a video server. In such a configuration, the image quality of the output of the decoder can be varied by a control signal from the video server, so that the image quality can be deliberately degraded, while using the same content data that the video server has. A service of changing image quality and bandwidth according to the client can be realized. In addition, it is possible to provide a demo image for selecting a program while saving the network bandwidth resources. Further, since the required bandwidth in the CATV network can be reduced, it is possible to provide services such as emergency news that wants to increase the number of supported clients even if the image quality is lowered.

Here, as an example of an MPEG decoder for decoding video data compressed by MPEG as a method for changing the image quality of decoded (decompressed) video data output from the decoder, an inverse quantization method is used. Can be applied, more specifically, a method of changing the value of the inverse quantization coefficient itself, or a method of performing inverse quantization after further performing quantization with a coefficient larger than the appropriate inverse quantization coefficient. is there. Further, a method of varying IDCT (inverse DCT transform) coefficients or a method of further performing quantization and inverse quantization on output data is also applicable.

Further, according to the present invention, in response to a request from the above-mentioned video server, that is, a client connected to a CATV network, compressed digital video data stored in advance is transmitted via a network interface while being compressed. The plurality of CATs are provided by a video server so that a VOD service for a plurality of CATV networks can be realized.
For each of the V networks, between the digital network to which the video server is connected and the CATV network, the relay device, that is, a decoder for decoding compressed digital video data transmitted via the digital network;
And modulates the video data decoded by the decoder so that it can be received on the client side, and
It is also characterized in that a relay device having a modulator for transmitting to the ATV network is arranged.

In such a configuration, content is shared by a minimum number of video servers with respect to a plurality of CATV networks using an existing coaxial cable network, and the plurality of CAs are shared.
It is possible to provide a VOD service to a TV network.
Further, it is possible to provide the same image quality as having a video server in the CATV network.

In addition, a decoder is built in the video server, and the compressed video data of the video server itself is decoded by the built-in decoder and modulated by the modulator (arranged with the client). CATV
Existing CATV which is a video server-client network (in the form of channels in service)
It is also possible to adopt a configuration in which the data is transmitted to the network.

In such a configuration, on the client side, the channel is adjusted to the channel using the existing STB.
Since it is possible to receive the VOD service, there is no need to have a decoder for each client,
Can provide service.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 is a block diagram showing a configuration of a VOD system according to a first embodiment of the present invention.

In FIG. 1, the video server 10 has a VO
In order to provide the D service, the video data is compressed (encoded) by a predetermined compression method, for example, MPEG, and is stored in the HDD.
And storage media such as DVDs.

In the present embodiment, the video server 10 has a built-in decoder 101. In the video server 10, that is, the video server 10 with a built-in decoder, when transmitting the stored video data in response to a request from a client, the video data is not compressed and transmitted as in the related art, but is stored in the built-in decoder. 101 decodes (restores) the original video data.

Further, in the present embodiment, the video data decoded by the decoder 101 is transmitted to a server (video server 1).
0) -C forming an analog network between clients
A multiplex modulation is performed by a modulator 102 built in the video server 10 so that the data can be transferred through the ATV network 11, and output to the CATV network 11 in the form of a channel in a CATV service negotiated with the client.

The STB 12 on the client side has a built-in demodulator 121 having the same function as the built-in demodulator 921 in the STB 92 shown in FIG. 11
The demodulator 121 separates and demodulates only the data of the requested channel from the multiplexed video data signal (video signal) transferred via And S
The TB 12 sends the separated and demodulated video signal to a display device 14 (realized by a television receiver or the like) via a cable 13.

In the VOD system having the above configuration,
Each STB 12 is provided with (ST in the prior art shown in FIG. 10).
Since no decoder is required (unlike B920),
Inexpensive V by video server using existing CATV network
OD service can be provided. In addition, since the video server 10 has the decoder (101),
Maintenance of the decoder is facilitated. Further, the video server 10
The existing CATV network (coaxial cable network) for the CATV service system can be used as it is for the network connecting the client and the client, and the STB 12 for the existing CATV service system as shown in FIG.
(STB92) can be used.

[Second Embodiment] In the VOD system according to the first embodiment, although an inexpensive VOD service can be provided, since the data output from the video server 10 is decoded data, the data amount is small. The use efficiency of the network (CATV network 11) decreases and the signal propagates over a coaxial cable, so that it is necessary to transmit over a long distance as in a system supporting a large-scale network (large-scale CATV network 11). In some cases, image quality is degraded. Therefore, a second embodiment for realizing long-distance transmission without deteriorating image quality while enabling provision of an inexpensive VOD service will be described.

FIG. 2 shows a VO according to a second embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of a D system, and the same parts as those in FIG. In FIG. 2, the video server 20 outputs the stored compressed video data as it is, that is, without decoding, and converts it into analog data so that the compressed video data can be transmitted efficiently without deteriorating the image quality. Output without conversion. To realize the output of such compressed digital video data, an AT
A network interface 201 for interfacing with a digital network (digital network) 21 typified by M or Ethernet is provided, and a configuration in which video data compressed from the interface 201 is transmitted to the digital network 21 is applied.

The digital network 21 includes a relay device 22
And is connected to the CATV network 11 via. The relay device 22 has a configuration for enabling the distribution of the video data signal by the CATV network 11 and for enabling the STB 12 to use the STB for the existing CATV service system.

FIG. 3 is a block diagram showing the configuration of the relay device 22. The relay device 22 is a digital network 21
Interface 221, a decoder 101 that decodes digital compressed video data received from the digital network 21 by the interface 221, and modulates the video data output by the decoder 101 for the CATV network 11. And a modulator 102 for transmission.

By providing the relay device 22 having the configuration shown in FIG. 3 between the digital network 21 and the CATV network 11,
The digital compressed video data transmitted from the video server 20 to the digital network 21 is decoded by the decoder 101 in the relay device 22, multiplex-modulated by the modulator 102, and the CATV agreed with the client.
CATV network 11 in the form of channels in service
Can be output to

The STB 12 on the client side uses a CATV
The demodulator 121 separates and demodulates only the data of the requested channel from the multiplexed video data signal (video signal) transferred via the network 11. The STB 12 transmits the separated and demodulated video signal to the cable 13.
To the display device 14 via the.

In such a configuration, the decoder is separated from the video server, and the video server and the decoder are connected via a digital network, that is, (the decoder with a built-in decoder applied in the first embodiment). By applying a decoder-connected video server (different from a video server), it is possible to reduce the distance between the decoder and the client and prevent the deterioration of image quality in the CATV network that transfers the output of the decoder.

In the system shown in FIG. 2, only one relay device 22 is provided between the digital network 21 and the CATV network 11. However, when the client is a remote apartment, By providing the relay device 22 for each apartment house, that is, by providing a set of the decoder 101 and the modulator 102 for each apartment house, the distance over which the decoded video data signal actually propagates through the CATV network 11 is shortened. And the deterioration of the image quality can be further prevented.

[Third Embodiment] The description of the first and second embodiments described above is omitted, but the decoder 101
Can be controlled from the video server (video server 10 or 20). At that time, the quality of the decoded image can be changed according to the client. Therefore, an embodiment (third embodiment) of a decoder capable of controlling the quality of an image from the video server 10 or 20 will be described with reference to the drawings.

FIG. 4 is a block diagram showing a schematic configuration of the decoder according to the embodiment. The decoder 101 in FIG.
The decoding circuit 101a that decodes the compressed digital video data as the input 41 and the decoding circuit 101a that receives the control signal 42 from the video server (10 or 20) control the decoding circuit 101a.
And a control circuit 101b for varying the quality of the decoded video data image, which is the output 43 of the data 01a.

In the decoder 101 having such a configuration, the control signal 4 from the video server (10 or 20) is output.
2, the control circuit 101b operates the decode circuit 101a.
, The quality of the image of the video data decoded by the decoding circuit 101a can be changed and output to the CATV network 11 via the modulator 102. At this time, it is possible to secure a band corresponding to the image quality, narrow the band of a video having poor image quality, and provide more types of content. As described above, by controlling the decoder 101 from the video server (10 or 20), the video server can provide images of different qualities only by having one content.

A detailed configuration example of the decoder 101 is as follows.
FIG. 5 shows an example of an MPEG decoder. The decoding circuit 101a includes a DMUX (separator) 51, VLDs (variable length decoding units) 52a and 52b, and an IQ (inverse quantization unit) 5.
3, an MC (motion compensator) 55 and an FM (frame memory) 56 have a well-known configuration.

The feature of the decoder 101 shown in FIG. 5 is that the control circuit 101b performs inverse quantization in an IQ (inverse quantization unit) 53 in the decode circuit 101a based on a control signal 42 from the video server (10 or 20). By changing the method (1), the image quality is varied (deteriorated). Here, to change the inverse quantization method, a method of changing the value of the inverse quantization coefficient itself, or a method of performing further quantization with a coefficient larger than the appropriate inverse quantization coefficient and then performing inverse quantization is used. Applicable.

The decoder 101 comprises a decoding circuit 101a 'and a control circuit 101b' as shown in FIG. 6, and the control circuit 101b 'controls the decoding circuit 101a'.
It is also possible to change (degrade) the image quality by changing the method of the IDCT in the IDCT (inverse DCT transform unit) 54 in the above. Here, to change the method of IDCT,
A method of changing the CT coefficient, that is, a method of cutting or reducing high-frequency components of the IDCT matrix is applicable.

In addition, the decoder 101 is composed of a decoding circuit 101a "and a control circuit 101b 'as shown in FIG. 7, and Q / IQ for performing quantization / inverse quantization of output data at the output side of the decoding circuit 101a". (Quantization / inverse quantization unit) 57 is provided, and the Q / IQ 47 is
0 or 20), the image quality can be varied (deteriorated) by controlling the control circuit 101b ″ based on the control signal 42. Specifically, the output data after decoding is controlled. Quantization is performed by a Q / IQ (quantization / inverse quantization unit) 57 using a value corresponding to the degree of deterioration indicated by the signal 42, and then the Q / IQ (quantization / inverse quantization unit)
By performing inverse quantization at 57, output data is reduced and the image quality is varied (deteriorated).

Fourth Embodiment In the second embodiment, a VOD system in which one video server supports one CATV network has been described. However, the present invention is not limited to this. Therefore, an embodiment (fourth embodiment) of a VOD system capable of supporting a plurality of CATV networks by one video server will be described with reference to the drawings.

FIG. 8 is a block diagram showing the configuration of the VOD system according to the embodiment. In the system shown in FIG. 8, the video server 20 is connected to a plurality of CATV networks, for example, three CATV networks 11A, 11B, and 11C by a digital network 21 that is fast and has no quality deterioration. In one CATV network, for example, the CATV network 11A, a relay device 22 applied in the second embodiment, that is, a relay device 22 having a network interface 221, a decoder 101, and a modulator 102 is additionally arranged in an existing system. ing. Such an arrangement of the relay device 22 is similarly made in the other CATV networks 11B and 11C.

In the system shown in FIG. 8, if the capacity of the server 20 is sufficiently large, the VOD service can be provided in each of the plurality of CATV networks 11A, 11B and 11C, even though the server is one video server 20. . In other words, a CATV network using a plurality of existing coaxial cables is
One video server 20 can support the image without deteriorating the image quality. This system is particularly suitable for small-scale CATs,
This is suitable when the V network is served from one video server.

[0049]

As described above in detail, according to the present invention, a relay device containing a decoder is arranged between a video server and a client, and compressed digital video data is connected on a digital network connecting a video server and a decoder. The data is transferred as it is, and the data is decoded by the decoder at the relay point, modulated by the modulator and transmitted to the CATV network. Therefore, it is not necessary to have a decoder for each client, and the STB and the The cable network can be used as it is, and the VOD service can be provided at low cost.

Further, since the compressed video data is transferred between the video server and the decoder, the image quality is not degraded and the distance between the decoder and the client can be shortened. Deterioration can also be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a VOD system according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a VOD system according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a relay device 22 in FIG. 2;

FIG. 4 is a block diagram showing a schematic configuration of a decoder according to a third embodiment of the present invention;

FIG. 5 is a block diagram showing a first detailed configuration example of the decoder of FIG. 4;

FIG. 6 is a block diagram showing a second detailed configuration example of the decoder in FIG. 4;

FIG. 7 is a block diagram showing a third detailed configuration example of the decoder in FIG. 4;

FIG. 8 is a block diagram showing a configuration of a VOD system according to a fourth embodiment of the present invention.

FIG. 9 is a block diagram showing a configuration of a general CATV service system using a CATV network.

FIG. 10 is a block diagram showing a configuration of a conventional VOD system using an existing CATV network.

[Explanation of symbols]

 10, 20 video server 11, 11A to 11C CATV network 12 STB (set-top box) 14 display device 21 digital network 22 relay device 101 decoder 102 modulator 201, 221 network interface 101a, 101a ', 101a "... Decode circuit 101b, 101b', 101b"... Control circuit

Claims (4)

[Claims] 1. A video server for transmitting compressed digital video data stored in advance in a compressed state via a network interface in response to a request from a client connected to a CATV network, and transmitting from the video server. A digital network provided for transmission of the compressed digital video data, and a decoder provided between the digital network and the CATV network, for decoding the compressed digital video data transmitted through the digital network; and The video data decoded by the decoder is modulated so that it can be received on the client side,
A relay device having a modulator for transmitting to a TV network. 2. The video-on-demand system according to claim 1, wherein said decoder is configured to vary output image quality according to a control signal from said video server. 3. A plurality of CATV networks, and a video server for transmitting compressed digital video data stored in advance in a compressed state via a network interface in response to a request from a client connected to the CATV network. A digital network provided for transmitting compressed digital video data sent from the video server; and a digital network provided between the digital network and the CATV network for each of the plurality of CATV networks. A relay device having a decoder for decoding compressed digital video data transmitted through the decoder, and a modulator for modulating video data decoded by the decoder so as to be receivable on the client side and sending the modulated data to the CATV network. Video on, characterized by having Temand system. 4. In response to a request from a client connected to a CATV network, compressed video data stored in advance is transmitted from a video server to a digital network via a network interface while being compressed. The compressed digital video data transmitted through the digital network is transmitted to the digital network and the C
Decoding by a relay device arranged between the ATV network,
A method for providing a video-on-demand service, comprising modulating the data so as to be receivable on the client side and transmitting the modulated data to the CATV network.