JP2004282390A - Storage device and method for disusing frame - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a storage device and a frame disusing method by which storage capacity is secured while minimizing the deterioration of picture quality of contents information by setting the disuse priority of I frames lower than that of P frames and disusing frames in accordance with the disuse priority. <P>SOLUTION: A proxy cache device 20 is provided with a storage means for storing a GOP (group of pictures) including I frames allowed to be independently reproduced and P frames allowed to be reproduced by forward prediction and constituted so as to reproduce the I frames and the P frames in order, a priority setting means for setting the disuse priority of the I frames lower than that of the P frames and a frame disusing means for disusing the frames constituting the GOP in accordance with the disuse priority when the storage capacity of the storage means is short. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a storage device and a frame discarding method for discarding stored moving image unit information when a storage capacity is insufficient.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a storage device such as a cache server stores content information (such as a moving image that can be downloaded from a server) stored in the storage device and includes a plurality of frames, and sets a discard priority for each frame. Was. Further, when the storage capacity of the storage device becomes insufficient, the storage device discards the frames in descending priority order so that the (important) frames with low discard priority are not discarded. The storage capacity was secured.
[0003]
Here, the conventional methods for setting the discard priority include a method based on the time information of the frame, a method based on the content of the content information, a method based on the resolution of the frame, and the like (for example, Patent Document 1).
[0004]
[Patent Document 1]
JP 2000-209258 A
[Problems to be solved by the invention]
By the way, some content information can be decomposed into frames for each reproduction time, and even if some frames are lost, the integrity of the entire content information is not lost.
[0006]
To be more specific, the content information constituted by the MPEG format will be described as an example. Such content information includes an I frame that can be independently reproduced, a P frame that can be reproduced by forward prediction, and bidirectional prediction. It is composed of a plurality of GOPs (Group of Pictures) including reproducible B frames.
[0007]
Here, in the case of a P frame or a B frame, if a frame serving as a reference for forward prediction or bidirectional prediction is discarded first, an image of the frame is not accurately reproduced and image quality is significantly deteriorated.
[0008]
On the other hand, even if it is a P frame or a B frame, the image quality of the frame does not deteriorate unless the frame serving as the reference for forward prediction or bidirectional prediction is discarded first. In addition, even if the P frame and the B frame are discarded, the image quality of the I frame does not deteriorate.
[0009]
However, the conventional storage device does not set the discard priority based on the type of the frame (such as an I frame, a P frame, or a B frame in MPEG). There is a problem that the image quality of a frame that can be reproduced by forward prediction or bidirectional prediction is deteriorated by being discarded first.
[0010]
Therefore, the present invention has been made in view of the above-described problem, and the discard priority of a frame that can be reproduced independently is set lower than the discard priority of a frame that can be reproduced by performing forward prediction or bidirectional prediction. It is an object of the present invention to provide a storage device and a frame discarding method capable of securing a storage capacity while minimizing deterioration of image quality of content information by setting and discarding a frame according to a discard priority. And
[0011]
[Means for Solving the Problems]
According to a first feature of the present invention, a storage device includes a first frame that can be independently reproduced and a second frame that can be reproduced by forward prediction, and is configured to reproduce the first frame and the second frame in this order. Storage means for storing moving image unit information, priority setting means for setting the discard priority of the first frame lower than the discard priority of the second frame, and discard when the storage capacity of the storage means is insufficient. The gist of the present invention is to provide a frame discarding unit for discarding a frame constituting the moving picture unit information according to the priority.
[0012]
According to this feature, the storage device discards the second frame before the first frame when the storage capacity of the storage device is insufficient, so that the first frame serving as the reference for forward prediction is discarded first. As a result, the storage capacity of the storage device can be secured while preventing the image quality of the second frame from being significantly degraded.
[0013]
According to a second feature of the present invention, in the first feature of the present invention, the priority setting means reproduces the discard priority of the second frame configured to be reproduced first after the second frame. The point is that the priority is set lower than the discarding priority of the second frame configured to perform the setting.
[0014]
According to this feature, the storage device discards the second frame that is configured to be reproduced after the second frame before the second frame that is configured to be reproduced first, The storage capacity of the storage device can be secured while preventing the image quality of the second frame configured to be reproduced later by discarding the second frame serving as the reference for forward prediction first.
[0015]
According to a third feature of the present invention, in the first or second feature of the present invention, in addition to the first frame and the second frame, the moving image unit information includes a third frame that can be reproduced by bidirectional prediction. The priority setting means is configured to reproduce the third frame, which is configured to be reproduced first, after the third frame, and to discard the same priority as the second frame serving as the reference for bidirectional prediction. The point is to set the degree.
[0016]
According to this feature, the storage device determines the same discard priority as the second frame having the highest discard priority among the second frames that are the basis of bidirectional prediction when the third frame is processed. , The storage capacity of the storage device can be secured while preventing the image quality of the third frame from being significantly degraded due to the discard of the second frame, which is the reference for bidirectional prediction, first.
[0017]
A fourth feature of the present invention is that a storage device that stores a GOP composed of an I frame, a P frame, and a B frame in MPEG performs a frame discarding method of discarding a frame. Setting a discard priority according to the type of the P frame and the B frame; and, when the storage capacity of the storage device is insufficient, discarding the frame according to the discard priority. That is the gist.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
The outline of the proxy cache device 20 in the present embodiment will be described with reference to the drawings. FIG. 1 is a schematic diagram illustrating an environment in which a proxy cache device 20 according to the present embodiment is installed.
[0019]
As shown in FIG. 1, the proxy cache device 20 is connected to client terminals (10a to 10c), and a server device 50 via a router 30 and an Internet communication network 40. Note that the proxy cache device 20 in the present embodiment is a storage device.
[0020]
The client terminal 10 transmits a content information request (delivery request) stored in the server device 50 and configured by a plurality of pieces of moving image unit information (for example, a GOP in MPEG) to the server device 50 via the proxy cache device 20. The content information is received from the proxy cache device 20 or the server device 50. Here, the client terminal 10 is a personal computer, a mobile phone, or the like.
[0021]
Here, the request includes the identifier of the content information and the required quality required for the content information. The required quality may be set by the client or may be determined by restrictions imposed by the communication network. The restriction by the communication network is, for example, the maximum communication performance (for example, 8 Mbps) of the ADSL line when the client terminal 10 is connected to the ADSL line.
[0022]
When receiving the request for the content information from the client terminal 10, the proxy cache device 20 checks whether the content information specified by the identifier of the content information included in the request is stored in the proxy cache device 20.
[0023]
Here, the proxy cache device 20 transmits the request received from the client terminal 10 to the server device 50 when the content information is not stored, and transmits the request of the content information when the content information is stored. The quality is compared with the required quality received from the client terminal 10.
[0024]
The proxy cache device 20 transmits the content information to the client terminal 10 when the quality of the content information satisfies the required quality, and transmits the content information to the client terminal 10 when the quality of the content information does not satisfy the required quality. Is transmitted to the server device 50.
[0025]
The proxy cache device 20 transmits the content information received from the server device 50 to the client terminal 10 and stores the received content information.
[0026]
The router 30 is connected to the client terminal 10, the proxy cache device 20, and the Internet communication network 40, and has a function of an ordinary router. Note that the router 30 may be a base station when the client terminal 10 is a mobile terminal.
[0027]
The Internet communication network 40 connects the router 30 and the server device 50, and may be a packet communication network or the like.
[0028]
The server device 50 stores the content information, and transmits the stored content information to the proxy cache device 20 in response to a request from the client terminal 10.
[0029]
(Configuration of proxy cache device)
The configuration of the proxy cache device 20 according to the present embodiment will be described with reference to the drawings. FIG. 2 is a block diagram of the proxy cache device 20 according to the present embodiment. FIG. 3 is a diagram illustrating an example of content information stored in the memory unit 22 according to the present embodiment.
[0030]
In the following, only the configuration required for the operation of the proxy cache device 20 to store the content information received from the server device 50 will be described.
[0031]
As shown in FIG. 2, the proxy cache device 20 includes a transmission / reception unit 21, a memory unit 22, a control unit 23, a content information management unit 24, a priority setting unit 25, and a frame discarding unit 26. .
[0032]
The transmission / reception unit 21 receives the content information from the server device 50 and transmits the content information to the client terminal 10.
[0033]
The memory unit 22 is a storage unit that stores the content information received by the transmission / reception unit 21. Further, the memory unit 22 may store a plurality of pieces of received content information.
[0034]
Specifically, the memory unit 22 stores content information configured as shown in FIG. Here, one piece of content information is composed of N GOPs, and one GOP is composed of 15 frames. Note that the number of frames in a GOP is not limited to 15, but may be any number.
[0035]
The frame types include an I-frame that can be reproduced independently, a P-frame that can be reproduced by forward prediction, and a B-frame that can be reproduced by bidirectional prediction. It indicates that. Here, the P frame and the B frame can be freely set for each GOP, and the I frame is configured to be reproduced first in the GOP.
[0036]
In this embodiment, a GOP is image information, an I frame is a first frame, a P frame is a second frame, and a B frame is a third frame. Further, the content information is not limited to the one configured in the MPEG format.
[0037]
The control unit 23 controls the transmission / reception unit 21 and the memory unit 22. Specifically, the control unit 23 searches the content information stored in the memory unit 22 for the same content information as the content information received by the transmission / reception unit 21, and stores the same content information in the memory unit 22. If it is stored, the searched content information (old content information) is discarded. That is, the free space of the memory unit 22 is increased by the amount of the discarded content information (old content information).
[0038]
If the capacity of the received content information is smaller than the free space of the memory unit 22, the control unit 23 stores the received content information in the memory unit 22. If the capacity of the received content information is larger than the free space of the memory unit 22, the control unit 23 calculates the content necessary for storing the received content information (the capacity that must be discarded). Instruct the information management unit 24.
[0039]
When instructed by the control unit 23, the content information management unit 24 calculates the received “capacity to be discarded”.
[0040]
Specifically, the content information management unit 24 manages the reproduction time, the total data amount, the average bit rate, the frame configuration, the average frame size for each frame type, and the like of the content information stored in the memory unit 22. The “capacity that must be discarded” is calculated based on these pieces of information.
[0041]
The frame configuration is the configuration of GOP (1) in FIG. 3, and the average frame size for each frame type is information such as 4000 bytes for an I frame and 800 bytes for a P frame.
[0042]
The priority setting unit 25 is a priority setting unit that sets the discard priority based on the frame type (I frame, P frame, B frame) and the order in which the frames are reproduced.
[0043]
Specifically, the priority setting unit 25 sets the highest discard priority “1” in the fifteenth P frame, taking GOPs (1) to (3) in FIG. 3 as an example, The fifteenth P frame is set to the same discard priority "1" as the fifteenth P frame to the fourteenth B frame which is a reference for bidirectional prediction. Next, the priority setting unit 25 sets a discard priority “2” lower than the fifteenth P frame to the thirteenth P frame. Similarly, the priority setting unit 25 sets the discard priority for the B frame of the twelfth frame to the P frame of the second frame. Finally, the priority setting unit 25 sets the lowest discard priority “11” to the first I frame. Further, the priority setting unit 25 may set discarding priorities “9” to “11” that are different for each GOP in the I frames of GOPs (1) to (3).
[0044]
The frame discarding unit 26 is a frame discarding unit that discards a frame (I frame, P frame, B frame) constituting the GOP according to the discarding priority set by the priority setting unit 25.
[0045]
Specifically, the frame discard unit 26 determines the discard priority of the frame to be discarded according to the “capacity to be discarded” calculated by the content information management unit 24, and Discard frames based on
[0046]
For example, referring to FIG. 3, when the frame discarding unit 26 determines that the discarding priority of the frame to be discarded is “1” to “8”, the two frames GOP (1) to (N) are discarded. Discard all of the 15th to 15th frames. Here, when the length of the GOP is 1 second, if all of the second to fifteenth frames are discarded, the frame rate becomes one frame per second (1 fps).
[0047]
Further, when the frame discarding unit 26 determines that the discard priority of the frame to be discarded is “1” to “10”, it discards all the frames other than the first frame of GOP (1). Here, when the length of the GOP is 1 second, if all frames other than the first frame of GOP (1) are discarded, the frame rate becomes 1 frame (0.33 fps) in 3 seconds. .
[0048]
In the present embodiment, the proxy cache device 20 is a storage device, but the storage device may be provided in a personal computer, a mobile phone, or the like.
[0049]
(Operation of proxy cache device)
The operation of the storage device according to the present embodiment will be described with reference to the drawings. FIG. 4 is a flowchart showing the operation of the proxy cache device 20 in the present embodiment. In the present embodiment, the proxy cache device 20 is a storage device.
[0050]
As shown in FIG. 4, in step 11, the proxy cache device 20 receives the content information from the server device 50.
[0051]
In step 12, the proxy cache device 20 searches the content information stored in the proxy cache device 20 for the same content information as the received content information. If the search result indicates that the received content information is stored in the proxy cache device 20, the process proceeds to step 13. If the received content information is not stored in the proxy cache device 20, the process proceeds to step 14. move on.
[0052]
In step 13, the proxy cache device 20 discards the content information retrieved in step 12 (the content information stored in the proxy cache device 20).
[0053]
In step 14, the proxy cache device 20 compares the capacity of the received content information with the free space of the proxy cache device 20. If the capacity of the received content information is smaller than the free space, the process proceeds to step 18. If the capacity of the received content information is larger than the free space, the process proceeds to step 15.
[0054]
In step 15, the proxy cache device 20 calculates a capacity required to store the received content information (a capacity that must be discarded).
[0055]
In step 16, the proxy cache device 20 sets the discard priority for the frames (I frame, P frame, B frame) constituting the content information.
[0056]
More specifically, the proxy cache device 20 sets the highest discard priority “1” to the 15th P frame in the case of GOP (1) in FIG. The same discard priority "1" as the fifteenth P frame is set to the fourteenth B frame, which is a reference for bidirectional prediction. Next, the proxy cache device 20 sets a discard priority "2" lower than the Pth frame of the fifteenth frame to the Pth frame of the thirteenth frame. Similarly, the proxy cache device 20 sets the discard priority for the B frame of the twelfth frame to the P frame of the second frame. Finally, the proxy cache device 20 sets the lowest discard priority “11” to the first I frame.
[0057]
In step 17, the proxy cache device 20 determines the discard priority of the frame to be discarded according to the “capacity to be discarded” calculated in step 15, and assigns the frame based on the judgment result. Discard.
[0058]
More specifically, using GOP (1) in FIG. 3 as an example, when the proxy cache device 20 determines that the discard priority of a frame to be discarded is “1” to “6”, the GOP (1) ) To (N) are all discarded.
[0059]
In step 18, the proxy cache device 20 stores the received content information.
[0060]
(Operation and Effect of Storage Device in Present Embodiment)
According to the proxy cache device 20 of the present embodiment, the proxy cache device 20 discards the P frame or the B frame before the I frame when the storage capacity of the proxy cache device 20 becomes insufficient. The storage capacity of the proxy cache device 20 can be secured while preventing the image quality of the P frame or the B frame from being significantly degraded due to the discard of the I frame serving as the reference for bidirectional prediction first.
[0061]
Further, the proxy cache device 20 secures the storage capacity of the proxy cache device 20 while maintaining the image quality of the content information at a predetermined level, and stores new content information in the secured storage capacity. 20 can increase the probability of storing the content information requested from the client terminal 10 (cache hit rate) and provide the client terminal 10 with a service with a short response time.
[0062]
According to the proxy cache device 20 of the present embodiment, the proxy cache device 20 sets a P frame that is configured to be reproduced after the P frame ahead of a P frame that is configured to be reproduced first. In order to prevent the P frame, which is a reference for forward prediction, from being discarded first, the image quality of the P frame configured to be reproduced later is prevented from being significantly deteriorated, and the storage capacity of the storage device is reduced. Can be secured.
[0063]
According to the proxy cache device 20 of the present embodiment, the proxy cache device 20 performs the same discarding as the P frame having the highest discard priority among the P frames that are the basis of bidirectional prediction when the B frame is processed. Since the priority is set to the B frame, it is possible to secure the storage capacity of the storage device while preventing the image quality of the B frame from being significantly degraded due to the discard of the P frame serving as the reference for bidirectional prediction first.
[0064]
(Example of change)
In this modification, the proxy cache device 20 determines in step 11 in the above-described embodiment that the quality of the content information received from the server device 50 is higher than the quality requested from the client terminal 10. In order to reduce the required quality, the received content information frame is discarded. Here, the proxy cache device 20 operates in the same manner as steps 15 to 17 in the above-described embodiment.
[0065]
Specifically, the proxy cache device 20 compares the quality of the received content information with the required quality, and calculates the “capacity that must be discarded” in order to reduce the quality of the received content information to the required quality ( Step 15).
[0066]
Next, the proxy cache device 20 sets the discard priority for the frames (I frame, P frame, B frame) constituting the content information (see step 16).
[0067]
Finally, the proxy cache device 20 determines the discard priority of the frame to be discarded according to the “capacity to be discarded”, and discards the frame based on the determination result (see step 17). .
[0068]
The proxy cache device 20 according to this modification reduces the quality of the received content information to the required quality from the client terminal 10 when the content information is received from the server device 50. By storing the information, it is possible to prevent the free space of the proxy cache device 20 from decreasing.
[0069]
【The invention's effect】
According to the storage device and the frame discarding method of the present invention, the storage device sets the discard priority of a frame that can be reproduced independently to be lower than the discard priority of a frame that can be reproduced by forward prediction or bidirectional prediction. However, by discarding the frame according to the discard priority, it is possible to secure the storage capacity while minimizing the deterioration of the image quality of the content information.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an environment in which a proxy cache device 20 according to an embodiment is installed.
FIG. 2 is a block diagram of a proxy cache device 20 according to the embodiment.
FIG. 3 is a diagram showing a configuration of content information stored in a proxy cache device 20 according to the embodiment.
FIG. 4 is a flowchart showing an operation of the proxy cache device 20 in the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Client terminal, 20 ... Proxy cache apparatus, 21 ... Transceiving part, 22 ... Memory part, 23 ... Control part, 24 ... Content information management part, 25 ... Priority Degree setting unit, 26: Frame discarding unit, 30: Router, 40: Internet communication network, 50: Server device

Claims (4)

A storage unit for storing moving image unit information including a first frame that can be played independently and a second frame that can be played back by forward prediction, and configured to play back the first frame and the second frame in this order; ,
Priority setting means for setting the discard priority of the first frame lower than the discard priority of the second frame;
A storage device comprising: a frame discarding unit that discards a frame constituting the moving image unit information according to the discard priority when the storage capacity of the storage unit is insufficient. The priority setting means may be configured to reproduce the discard priority of the second frame that is configured to be reproduced first and the discard priority of the second frame that is configured to be reproduced after the second frame. The storage device according to claim 1, wherein the storage device is set to be lower than the temperature. The video unit information includes a third frame that can be reproduced by bidirectional prediction, in addition to the first frame and the second frame,
The priority setting means is configured to reproduce the third frame that is configured to be reproduced first, after the third frame, and is configured to be the same as the second frame that is a reference for the bidirectional prediction. 3. The storage device according to claim 1, wherein a discard priority is set. A storage device for storing a GOP including an I frame, a P frame, and a B frame in MPEG is a frame discarding method for discarding a frame,
The storage device setting a discard priority according to the types of the I frame, the P frame, and the B frame;
Discarding the frame in accordance with the discard priority when the storage capacity of the storage device is insufficient.

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