JP5476081B2 - Data transfer apparatus, communication system and control method - Google Patents

Description

  The present invention relates to a data transfer apparatus, a communication system, and a control method for transferring data in GOP (Group Of Picture) units.

  In recent years, as shown in FIG. 7, the digital broadcast data received by the server apparatus 1 ′ from the broadcast antenna 3 ′ or the like is stored in a buffer (not shown) in GOP units, and the digital broadcast data stored in the buffer in GOP units. There is a communication system in which data is transferred to a client terminal 2 ′ via a network (NW) and controlled to be output and displayed on the display device 4 ′ or the like at the client terminal 2 ′.

  However, in the communication system described above, depending on the state of the network (NW), the server device 1 ′ cannot transfer digital broadcast data to the client terminal 2 ′ via the network (NW), and the server device 1 ′. The digital broadcast data may stay in the buffer and a buffer overflow may occur.

  When a buffer overflow occurs, the server apparatus 1 ′ cannot store the digital broadcast data received from the broadcast antenna 3 ′ or the like in the buffer, and therefore discards the digital broadcast data received from the broadcast antenna 3 ′ or the like. become. After that, when the network (NW) condition is improved and data transfer to the client terminal 2 ′ becomes possible, the digital broadcast data staying in the buffer of the server device 1 ′ is transferred to the client terminal 2 ′, and the buffer overflow When this is resolved, new digital broadcast data received from the broadcast antenna 3 ′ or the like is stored in the buffer of the server device 1 ′.

  However, depending on the start timing of storing new digital broadcast data received from the broadcast antenna 3 ′ or the like in the buffer of the server apparatus 1 ′, the digital broadcast data at the head of the GOP cannot be stored in the buffer. There is a case where only a part of digital broadcast data constituting the GOP is stored in the buffer.

  GOP is the smallest playback / editing unit that composes MPEG (Moving Picture Expert Group), and is usually composed of about 15 frames of data. A GOP consisting of about 15 frames of data takes about 0.5 seconds. In the case of digital broadcasting, since there are 2-3 pieces of data per GOP per second, the start timing for storing new digital broadcasting data received from the broadcasting antenna 3 ′ or the like in the buffer of the server device 1 ′ Depending on the case, the digital broadcast data at the head of the GOP cannot be stored in the buffer. For this reason, there may occur a case where only a part of the digital broadcast data constituting one GOP is stored in the buffer.

  When output display is performed using all digital broadcast data constituting one GOP, the image quality of the digital broadcast data subjected to the output display can be guaranteed. However, when output display is performed using only a part of digital broadcast data constituting one GOP, the image quality of the digital broadcast data subjected to the output display cannot be guaranteed. Therefore, in order to guarantee the image quality of the digital broadcast data output and displayed on the transfer destination display device 4 ′ etc., it is necessary to store all the digital broadcast data constituting one GOP in the buffer of the server device 1 ′. There is.

  In addition, as a technical document filed prior to the present invention, there is a document that discloses a data interface circuit that interfaces image data that is predictively encoded between image processing devices in units of GOP (see, for example, Patent Document 1). ).

  In the above Patent Document 1, the control circuit (14) causes the FIFO circuit (12) to send the compressed image data (S2) via the selector circuit (10) when neither overflow nor underflow occurs in the FIFO circuit (12). Control to capture sequentially. Further, when underflow occurs, the FIFO circuit (12) is controlled so that the last GOP is repeatedly output without taking in data. When overflow occurs, the FIFO circuit (12) is controlled so as to take in the compressed image data (S1) via the selector circuit (10).

JP-A-8-223580

  In the above-mentioned patent document 1, when neither overflow nor underflow occurs in the FIFO circuit (12), the FIFO circuit (12) is controlled so as to sequentially take in the compressed image data (S2) via the selector circuit (10). Is disclosed. However, when the invention of Patent Document 1 is applied to digital broadcasting, there are cases where it is impossible to sequentially capture from the compressed image data (S2) at the beginning of the GOP. In this case, the compressed image data (S2) ) Cannot be guaranteed.

  In addition, when the invention of Patent Document 1 is applied to digital broadcasting, it is necessary to perform a GOP number detection process. In order to detect the GOP number, MPEG (Moving Picture Expert Group) 2-TS (Transport Stream) is divided into multiple ES (Elementary Stream) and the sequence header of video ES is detected from the divided multiple ES However, it is necessary to analyze the sequence header. For this reason, when the invention of Patent Document 1 is applied to digital broadcasting, the amount of processing performed by the FIFO circuit (12) increases.

The present invention has been made in view of the above circumstances, and an object thereof is to assure the image quality of data to be output and displayed on a transfer destination apparatus, which is the above-described problem .

  In order to achieve this object, the present invention has the following features.

<Data transfer device>
The data transfer device according to the present invention is:
Receiving means for receiving and storing data;
A buffer,
Control means for sequentially storing data stored in the receiving means in the buffer;
Transfer means for sequentially transferring data sequentially stored in the buffer via a network;
The control means includes
When the data stored in the receiving unit cannot be stored in the buffer, the data stored in the receiving unit starts to be discarded, and at least two GOP (Group Of Picture) units of data are stored. When it becomes possible to store the data in the buffer, the process of sequentially storing the data stored in the receiving unit in the buffer is started.

  According to the present invention, it is possible to guarantee the image quality of data output and displayed on the transfer destination device.

It is a figure which shows the system configuration example of the communication system of this embodiment. FIG. 3 is a first diagram for explaining an example of a data transfer processing operation in the communication system. FIG. 10 is a second diagram for explaining an example of the data transfer processing operation in the communication system. FIG. 10 is a third diagram for explaining an example of the data transfer processing operation in the communication system. 4 is a diagram illustrating an example of processing operation performed in the server device 1. FIG. It is a figure which shows the system configuration example of the communication system of this embodiment. It is a figure which shows the structural example of the communication system relevant to this invention.

<Outline of communication system>
First, an outline of a communication system according to the present embodiment will be described with reference to FIG.

  The communication system according to the present embodiment is a communication system that includes a server device 1 and at least one client terminal 2.

  The server device 1 according to the present embodiment includes a receiving unit (corresponding to the receiving unit 10) for receiving data, a buffer (corresponding to the transmitting buffer 13), and a control unit (stored in the buffer 13). And a transfer means (corresponding to the transmission unit 14) for transferring the data stored in the buffer 13 to the client terminal 2 via the network (NW). The control means 12 stores the data received by the receiving means 10 in the buffer 13 when at least two GOP (Group Of Picture) units of data can be stored in the buffer 13.

  As a result, all the data for one GOP unit can be securely stored in the buffer 13, so all the data for one GOP unit is transferred to the client terminal 2, and the transferred data It becomes possible to guarantee the image quality of the output image. Therefore, it is possible to guarantee the image quality of the data output and displayed on the client terminal 2 as the transfer destination. Hereinafter, the communication system of the present embodiment will be described in detail with reference to the accompanying drawings.

<System configuration example of communication system>
First, a system configuration example of a communication system according to the present embodiment will be described with reference to FIG.

  The communication system of the present embodiment is configured by connecting the server device 1 and the client terminal 2 via a network (NW). The server device 1 transfers the digital broadcast data received from the broadcast antenna 3 or the like to the client terminal 2 via the network (NW), and controls the client terminal 2 to output and display the digital broadcast data on the display device 4 or the like. To do.

  The server device 1 according to the present embodiment includes a receiving unit 10, a receiving buffer 11, a control unit 12, a transmitting buffer 13, and a transmitting unit 14.

  The receiving unit 10 sequentially receives digital broadcast data from the broadcast antenna 3 and the like, and stores the sequentially received digital broadcast data in the reception buffer 11 in units of GOPs.

  The reception buffer 11 temporarily stores digital broadcast data sequentially received by the reception unit 10. The control unit 12 stores the digital broadcast data sequentially stored in the reception buffer 11 in the transmission buffer 13 in GOP units.

  GOP is the minimum playback / editing unit that composes MPEG, and usually consists of about 15 frames. For example, the GOP is composed only of I frames. Also, it is configured by a combination of an I frame, a P frame, and a B frame. Further, it is configured by a combination of an I frame and a P frame or a B frame.

  The I frame is an intra-encoded image in which image data is compression-encoded by predictive encoding and data of another encoded image (frame) is not required for decoding. The P frame is a forward predictive encoded image that requires a decoded frame immediately before in decoding. The B frame is a bi-directional predictive encoded image that requires a decoded frame immediately before and immediately after decoding.

  The server device 1 of the present embodiment stabilizes the image quality of digital broadcast data by buffer management based on the data amount in GOP units.

  The transmission buffer 13 temporarily stores digital broadcast data in GOP units. The transmission unit 14 transfers the digital broadcast data stored in the transmission buffer 13 to the client terminal 2. The transmission unit 14 has a transmission function using IP, and transfers the digital broadcast data stored in the transmission buffer 13 to the client terminal 2 via the network (NW).

  The client terminal 2 displays the digital broadcast data transferred from the server device 1 on the display device 4 or the like. The client terminal 2 of the present embodiment includes a receiving unit 21, a receiving buffer 22, and a control unit 23.

  The receiving unit 21 receives the digital broadcast data transferred from the server device 1 and stores the received digital broadcast data in the reception buffer 22. The reception buffer 22 temporarily stores digital broadcast data. The control unit 23 outputs the digital broadcast data stored in the reception buffer 22 to the display device 4 or the like. The control unit 23 displays the digital broadcast data on the display device 4 of the client terminal 2, or displays the digital broadcast data on the external display device 4.

<Example of processing operation in communication system>
Next, a processing operation example in the communication system of the present embodiment will be described with reference to FIGS.

<When the network is in good condition>
First, the case where the network state between the server apparatus 1 and the client terminal 2 is good will be described with reference to FIG.

  When the network state is good, the digital broadcast data can be transferred from the server device 1 to the client terminal 2 without delay as shown in FIG. In this case, a small amount of digital broadcast data is stored in the buffers 11, 13, and 22 of both the server device 1 and the client terminal 2.

<In case of poor network status>
Next, a case where the network state between the server apparatus 1 and the client terminal 2 is in a bad state will be described with reference to FIG.

  When the network state is bad, as shown in FIG. 3, the digital broadcast data cannot be transferred from the server device 1 to the client terminal 2 without delay, and the server device 1 does not transfer data to the client terminal 2. It will stop (transfer stop). As a result, the amount of data in the reception buffer 22 of the client terminal 2 becomes empty, and the digital broadcast data cannot be output and displayed on the display device 4 or the like (cannot be displayed).

  Further, since the server apparatus 1 cannot transfer data to the client terminal 2, the digital broadcast data stays in the transmission buffer 13. As a result, there is no free space in the transmission buffer 13, a buffer overflow occurs, new digital broadcast data received from the broadcast antenna 3 or the like cannot be stored in the transmission buffer 13, and the digital broadcast data is discarded. (Discard data).

<When the network status is restored from a poor state to a good state>
Next, a case where the network state between the server apparatus 1 and the client terminal 2 is restored will be described with reference to FIG.

  When the network state is restored, the server apparatus 1 can resume data transfer to the client terminal 2 as shown in FIG. In this case, the server device 1 transfers the digital broadcast data staying in the transmission buffer 13 to the client terminal 2 (sequential transfer), and the client terminal 2 outputs and displays the new digital broadcast data on the display device 4 or the like. (Sequential display).

  Further, the server apparatus 1 transfers the digital broadcast data staying in the transmission buffer 13 to the client terminal 2, and there is a free capacity in the transmission buffer 13. As a result, the buffer overflow of the transmission buffer 13 is eliminated, and new digital broadcast data received from the broadcast antenna 3 or the like can be stored in the transmission buffer 13.

  However, depending on the start timing of storing new digital broadcast data received from the broadcast antenna 3 or the like in the transmission buffer 13, it is not possible to store in the transmission buffer 13 from the digital broadcast data at the head of the GOP. There may occur a case where only a part of the digital broadcast data constituting the data is stored in the transmission buffer 13. FIG. 4 shows a case where a part of the digital broadcast data having the GOP number 14 is stored in the transmission buffer 13.

  When output display is performed on the display device 4 or the like using only a part of digital broadcast data constituting one GOP, the image quality of the digital broadcast data subjected to the output display cannot be guaranteed. Therefore, in order to guarantee the image quality of the digital broadcast data output and displayed on the display device 4 or the like, it is necessary to store all the digital broadcast data constituting one GOP in the transmission buffer 13.

  Therefore, the server apparatus 1 of the present embodiment stores at least two GOP units of digital broadcast data in the transmission buffer 13 in order to store in the transmission buffer 13 all the digital broadcast data constituting one GOP. When it is possible, new digital broadcast data received from the broadcast antenna 3 or the like is stored in the transmission buffer 13.

  As a result, the server device 1 of the present embodiment can reliably store all digital broadcast data for one GOP unit in the transmission buffer 13 even when the buffer overflow of the transmission buffer 13 frequently occurs. Become. As a result, it is possible to transfer all the digital broadcast data for one GOP unit to the client terminal 2 and to guarantee the image quality of the output image of the transferred digital broadcast data. Therefore, it is possible to guarantee the image quality of the digital broadcast data output and displayed on the client terminal 2 as the transfer destination.

<Processing example of server device 1>
Next, an example of processing operation performed by the server device 1 of the present embodiment will be described with reference to FIG.

  The control unit 12 sets the buffer insertion flag to ON when starting data transfer to the client terminal 2 (step A1). Further, the control unit 12 sets the estimated bit rate to a default value (step A2).

  The buffer insertion flag is a flag for determining whether or not a buffer overflow has occurred in the transmission buffer 13. In this embodiment, when the buffer insertion flag is ON, it means that the buffer overflow has not occurred, and when the buffer insertion flag is OFF, it means that the buffer overflow has occurred. .

  The estimated bit rate is a value used when determining whether or not the free capacity of the transmission buffer 13 is equal to or larger than the data amount corresponding to two GOP units, and if the free capacity of the transmission buffer 13 is equal to or larger than the estimated bit rate. For example, it is determined that the free capacity of the transmission buffer 13 is equal to or larger than the data amount corresponding to two GOP units. If the free capacity of the transmission buffer 13 is not equal to or greater than the estimated bit rate, it is determined that the free capacity of the transmission buffer 13 is not equal to or greater than the data amount corresponding to two GOP units. As the default value, a value defined in advance according to the broadcast type (terrestrial digital broadcast, CS broadcast, BS broadcast) of data to be transferred is used.

  Next, the control unit 12 acquires digital broadcast data from the reception buffer 11 (step A3), and updates the estimated bit rate based on the acquired digital broadcast data (step A4). The updated estimated bit rate is calculated by the following formula.

  N represents a period for calculating the weighted average. The weighting coefficient n is a value for weighting the received data amount n per second, and is set to satisfy the following condition.

  The received data amount n per second means the amount of data received by the server device 1 from the broadcast antenna 3 during a period in which [the extraction time when the digital broadcast data is extracted from the reception buffer 11]-[current time] is n. [] Indicates a Gaussian symbol. However, the second received data amount n uses an initial value for a period in which the server device 1 is not receiving data from the broadcast antenna 3. The initial value of the received data amount n per second is the specified maximum bit rate / margin count. The specified maximum bit rate is 21 Mbps for terrestrial digital broadcasting and 24 Mbps for BS / CS digital broadcasting. The margin count is a value for weighting the estimated bit rate, and is a value of 1 or more.

  The control unit 12 determines whether or not the buffer insertion flag is ON (step A5). If the buffer insertion flag is ON (step A5 / Yes), the buffer overflow of the transmission buffer 13 has not occurred. To determine whether there is free space in the transmission buffer 13 (step A6).

  When there is no free space in the transmission buffer 13 (step A6 / Yes), the control unit 12 cannot store the digital broadcast data acquired from the reception buffer 11 in the transmission buffer 13, and therefore discards the digital broadcast data. (Step A7), the buffer insertion flag is set to OFF (Step A8).

  If there is free space in the transmission buffer 13 (step A6 / No), the digital broadcast data acquired from the reception buffer 11 is stored in the transmission buffer 13 (step A9).

  Further, when the buffer insertion flag is OFF (step A5 / No), the control unit 12 determines that a buffer overflow has occurred, and the free capacity of the transmission buffer 13 is equal to or greater than the estimated bit rate calculated in step A4. Whether or not (step A10).

  If the free capacity of the transmission buffer 13 is equal to or greater than the estimated bit rate (step A10 / Yes), the buffer insertion flag is set to ON because the free capacity of the transmission buffer 13 is equal to or larger than the data amount corresponding to two GOP units. (Step A11), the digital broadcast data acquired from the reception buffer 11 is stored in the transmission buffer 13 (Step A9).

  If the buffer free capacity is not equal to or greater than the estimated bit rate (step A10 / No), the free capacity of the transmission buffer 13 is not greater than the data amount corresponding to two GOP units, and the digital broadcast data is discarded. (Step A12).

  As a result, after the buffer overflow of the transmission buffer 13 occurs, the control unit 12 performs the digital broadcast obtained from the reception buffer 11 until it can store at least two GOP units of data in the transmission buffer 13. Data will be discarded. When at least two GOP units of data can be stored in the transmission buffer 13, the digital broadcast data acquired from the reception buffer 11 is stored in the transmission buffer 13. As a result, since the control unit 12 stores all the digital broadcast data constituting the GOP1 unit in the transmission buffer 13, the digital broadcast data constituting the GOP1 unit is output and displayed on the display device 4 or the like. Image quality can be guaranteed.

<Operation / Effect of Server Device 1 of this Embodiment>
As described above, the server device 1 according to the present embodiment allows the reception buffer 11 when the free capacity of the transmission buffer 13 becomes a data amount corresponding to two GOP units after the buffer overflow of the transmission buffer 13 occurs. Is stored in the transmission buffer 13. As a result, even when buffer overflow of the transmission buffer 13 frequently occurs, digital broadcast data for one GOP unit can be reliably stored in the transmission buffer 13. As a result, all the data for one GOP unit can be transferred to the client terminal 2 and the image quality of the output image of the transferred data can be guaranteed.

  Further, the server device 1 according to the present embodiment determines whether or not the free capacity of the transmission buffer 13 has reached a data amount corresponding to two GOP units using the estimated bit rate. As a result, it is possible to determine whether or not the free capacity of the transmission buffer 13 has reached a data amount corresponding to two GOP units without performing GOP detection processing. Can be reduced.

  Currently, wireless LAN communication is performed using the ISM (Industry Science Medical) band near the 2.4 GHz band. However, the ISM band is also used for Bluetooth, Zigbee, microwave ovens, cordless phones, etc. in addition to wireless LAN.

  For this reason, a radio wave generator (Bluetooth, Zigbee, electronic) that uses at least part of the radio waves in the same frequency band as the wireless LAN during data transfer from the server device 1 to the client terminal 2 using the wireless LAN. When a range, cordless phone, etc.) generate radio waves, radio wave interference may occur, and there may be a frequent occurrence of a situation where data cannot be transferred from the server device 1 to the client terminal 2. If a situation in which data cannot be transferred from the server apparatus 1 to the client terminal 2 frequently occurs, a buffer overflow of the transmission buffer 13 frequently occurs as a result.

  However, since the server apparatus 1 according to the present embodiment can securely store the digital broadcast data for one GOP unit in the transmission buffer 13 even when the buffer overflow of the transmission buffer 13 frequently occurs, All data for one GOP unit can be transferred to the client terminal 2 and the image quality of the output image of the transferred data can be guaranteed.

  The above-described embodiment is a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above-described embodiment alone, and various modifications are made without departing from the gist of the present invention. Implementation is possible.

  For example, in FIG. 1, the server apparatus 1 is configured to be connected to one client terminal 2 via a network (NW). However, as shown in FIG. 6, the server apparatus 1 is connected to a plurality of client terminals 2-1, 2-2, 2-N (N is an arbitrary integer) via a network (NW). It is also possible to construct.

  In addition, the control operation in each device configuring the communication system in the present embodiment described above can be executed using hardware, software, or a composite configuration of both.

  In the case of executing processing using software, it is possible to install and execute a program in which a processing sequence is recorded in a memory in a computer incorporated in dedicated hardware. Alternatively, the program can be installed and executed on a general-purpose computer capable of executing various processes.

  For example, the program can be recorded in advance on a hard disk or ROM (Read Only Memory) as a recording medium. Alternatively, the program can be stored (recorded) temporarily or permanently in a removable recording medium. Such a removable recording medium can be provided as so-called package software. Removable recording media include floppy (registered trademark) disks, CD-ROM (Compact Disc Read Only Memory), MO (Magneto optical) disks, DVDs (Digital Versatile Discs), Blu-ray disks, magnetic disks, and semiconductor memories. Can be mentioned.

  The program is installed in the computer from the removable recording medium as described above. In addition, it is wirelessly transferred from the download site to the computer. In addition, it is transferred to the computer via a network by wire.

  In addition, the communication system in the present embodiment is not only executed in time series according to the processing operation described in the above embodiment, but also the processing capability of the apparatus that executes the processing, or in parallel or individually as required. It is also possible to build to run on

1 Server device (data transfer device)
10 Receiver (Receiving means)
11 reception buffer 12 control unit (control means)
13 Transmission buffer (buffer)
14 Transmitter (transfer means)
2 Client terminal 21 Reception unit 22 Reception buffer 23 Control unit NW network 3 Broadcast antenna 4 Display device

Claims (5)

Receiving means for receiving and storing data;
A buffer,
Control means for sequentially storing data stored in the receiving means in the buffer;
Transfer means for sequentially transferring data sequentially stored in the buffer via a network;
The control means includes
When the data stored in the receiving unit cannot be stored in the buffer, the data stored in the receiving unit starts to be discarded, and at least two GOP (Group Of Picture) units of data are stored. A data transfer apparatus, which starts a process of sequentially storing data stored in the receiving means in the buffer when it can be stored in the buffer. The control means includes
When the data stored in the receiving unit cannot be stored in the buffer, the data is stored in the receiving unit until at least two GOP units of data can be stored in the buffer. 2. The data transfer apparatus according to claim 1, wherein the data is sequentially discarded. The control means includes
It is determined whether or not the free space of the buffer is greater than or equal to the estimated bit rate based on an estimated bit rate that serves as an index for determining whether or not the free space of the buffer is equal to or greater than the data amount corresponding to two GOP units. 2. When the free capacity of the buffer is equal to or greater than the estimated bit rate, it is determined that at least two GOP units of data can be stored in the buffer. 2. The data transfer device according to 2. A communication system comprising a server device and at least one client terminal,
The server device
Receiving means for receiving and storing data;
A buffer,
Control means for sequentially storing data stored in the receiving means in the buffer;
Transfer means for sequentially transferring data sequentially stored in the buffer to the client terminal via a network;
The control means includes
When the data stored in the receiving unit cannot be stored in the buffer, the data stored in the receiving unit starts to be discarded, and at least two GOP (Group Of Picture) units of data are stored. A communication system characterized by starting a process of sequentially storing data stored in the receiving means in the buffer when it can be stored in the buffer. A control method performed by a transfer control device for transferring data,
A receiving step for receiving data and storing it in a receiving means;
A control step of sequentially storing data stored in the receiving means in a buffer;
A transfer step of sequentially transferring data sequentially stored in the buffer via a network;
The control step includes
When the data stored in the receiving unit cannot be stored in the buffer, the data stored in the receiving unit starts to be discarded, and at least two GOP (Group Of Picture) units of data are stored. A control method characterized by starting a process of sequentially storing data stored in the receiving means in the buffer when it can be stored in the buffer.

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