KR20060122784A - Method and apparatus for synchronizing data service with video service in digital multimedia broadcasting - Google Patents

Abstract

A method and an apparatus for providing a synchronized data service with a video service in digital multimedia broadcasting are provided to synchronize the information for representing a performance time of a specific event with the audio/video service. An AV(Audio/Video) signal source(200) generates audio and video contents. A DMB(Digital Multimedia Broadcasting) AV encoder(210) encodes the produced audio and video in order to fit the terrestrial DMB standard. A data server(230) performs various data services. An ensemble multiplexing member(240) multiplexes the generated AV stream and data packet as one ensemble. A DMB transmitting member(250) performs OFDM(Orthogonal Frequency Division Multiplexing) encoding and RF(Radio Frequency) transmission. An NTP(Network Time Protocol) server(220) performs exact temporal synchronization of the devices.

Description

Method and apparatus for providing data service synchronized with video service in digital multimedia broadcasting {Method and Apparatus for synchronizing data service with video service in Digital Multimedia Broadcasting}

1 is a configuration diagram of a conventional terrestrial DMB broadcast transmission system;

2 is a diagram showing the configuration of a terrestrial DMB broadcasting transmission system for synchronizing real-time video and data services according to an embodiment of the present invention;

3A is a view for explaining a method of calculating a time stamp (CTS) based time point at which data is to be reproduced;

3B is a view showing an example of the configuration of the data carousel shown in FIG. 3A,

3C is a diagram showing an example of the configuration of the synchronization metadata shown in FIG. 3A;

4 is a diagram showing the configuration of a terrestrial DMB broadcasting transmission system for synchronizing a real-time video and data service according to another embodiment of the present invention;

5 is a diagram showing the configuration of a terrestrial DMB broadcasting transmission system for synchronizing a real-time video and data service according to another embodiment of the present invention;

6 is a diagram showing the configuration of a terrestrial DMB broadcasting transmission system for synchronizing real-time video and data services according to another embodiment of the present invention;

7 illustrates a receiving system capable of data service synchronized with video according to the present invention.

The present invention relates to digital multimedia broadcasting (DMB), and more particularly, audio transmitted through encoding and multiplexing of MPEG-4 and MPEG-2 data transmitted based on Eureka-147 in digital multimedia broadcasting, and A method and apparatus for synchronizing to video (AV).

The synchronized data service model is intended to provide a means for an application program running on terrestrial DMB middleware to perform synchronized execution with other media such as a DMB video service. In this case, the video service refers to an AV service provided by the "Microwave Digital Radio Broadcasting Video Transceiver Matching Standard" (TTAS.KO-07.0026).

1 is an exemplary configuration diagram of a conventional terrestrial DMB broadcast transmission system.

When the audio / video signal source 100 generates a video signal and an audio signal for DMB broadcasting, the DMB AV encoder 110 generates an AV stream by encoding according to the DMB video transmission / reception standard. . This process includes the AV encoding process of MPEG-4 and the multiplexing process to MPEG-2 transport stream (TS). On the other hand, for the data service based on Eureka 147 (Euraka-147), the data signal source 130 generates a variety of data irrelevant to the audio / video (AV) signal, the data encoder 140 is a data signal source ( Various data generated from 130 are encoded to generate a data packet.

The AV stream and the packet data output from the DMB AV encoder 110 and the data encoder 140 are multiplexed by an ensemble transport interface standard (ETI frame) by the ensemble multiplexer 150 and then DMB. The transmitter 160 transmits a radio frequency (RF) signal through a process such as COFDM encoding.

Here, the ETI frame basically consists of a fast information channel (FIC) (hereinafter referred to as FIC) and a main service channel (MSC) (hereinafter referred to as MSC) data. This is generated by the FIC component 151 and the MSC component 152 in the ensemble multiplexer 150, respectively.

In the Eureka-147 system, the FIC channel is an information channel for quick access to provide multiplexing information and service information, and the MSC channel is used to multiplex service components corresponding to each service according to the multiplexing structure established through the FIC channel. Is the primary service channel.

Basic audio data, AV streams and various additional data are multiplexed and transmitted to the MSC. In the FIC, absolute time is inserted into FIG Type 0 Extended 10 (FIG 0/10) in the form of Universal Coordinated Time (UTC), which provides a reference time at which data of the MSC is decoded and reproduced. Therefore, this UTC absolute time information can be inserted as a reference of timing information when data is encoded.

In the MPEG-4 and MPEG-2 systems, reference clocks and time stamps are used to synchronize AV data transmitted by an elementary stream (ES) and to transmit timing information.

Time stamps in MPEG-4 use a decoding time stamp (DTS) to define a decoding time of access units in a decoding buffer in a receiving terminal, and a composition unit (CU) The composition time stamp (CTS) is used to accurately represent their composition time.

The Object Clock Reference (OCR) is used to send the time notation for a given stream to the ES decoder. The object reference clock (OCR) value corresponds to an Object Time Base (OTB) value at the time that the transmitting terminal generates an object reference clock (OCR) time stamp, and the object reference clock (OCR) values correspond to SL packet headers. Included in the transmission.

Domestic terrestrial DMB broadcasting uses MPEG-4 and MPEG-2 simultaneously. Here, in order to transmit and synchronize timing information of audio and video, PCR (Program Clock Reference) and PTS (Program Time Stamp) are used for MPEG-2, and object reference clock (OCR) for MPEG-4. The composition time stamp (CTS) and decoding time stamp (DTS) information are used. Also, for synchronization of MPEG-4 and MPEG-2, when the MPEG-4 SL packet is mapped to the MPEG-2 PES packet, it is 1: 1. The MPEG-2 PTS is the MPEG-4 SL packet header. If the object reference clock (OCR) is included in the PES header is included, otherwise the PTS is not used. The object time base (OTB), which defines the time notation for MPEG-4 data streams, also interlocks with the system time clock of MPEG-2.

Meanwhile, the data encoder 140 of FIG. 1 uses the multimedia object protocol (MOT), which is a data transmission standard based on the DMB system standard (Eureka-147), to encode the FIC channel for transmitting timing information. Refers to the UTC absolute time information transmitted. That is, the data encoder 140 objectizes data in units of files or directories, and then packetizes the data. In this case, a timestamp, which is timing information on a time when one data object is to be decoded and reproduced, is inserted into a header of the data object using UTC format. However, this method has a problem that it is difficult to achieve accurate synchronization between the DMB audio / video (AV) stream and the data.

The present invention has been proposed to solve the above problems, and in order to provide a synchronization data service with a DMB audio / video service in DMB broadcasting, information indicating a time at which a specific event in an application program is performed is synchronized with the audio / video service. It is an object of the present invention to provide a method and apparatus for a data service synchronized with a video service in digital multimedia broadcasting, which is generated and transmitted as possible.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

An apparatus according to the present invention for achieving the above object,

An AV encoder for encoding an AV signal according to the terrestrial DMB standard and providing an AV timestamp to the data server; A data server for generating synchronization metadata for providing a data service synchronized with an AV service using the AV timestamp; A time synchronization server for accurate time synchronization of the AV encoder and the data server; And means for multiplexing and transmitting the output signal of the AV encoder and the output signal of the data server.

The method according to the present invention for achieving the above object,

Receiving an AV time stamp for the AV data; Calculating a timestamp of the data at the time point at which the data is reproduced in the terminal based on the AV timestamp; Generating synchronization metadata comprising a timestamp of the calculated data; And encoding and transmitting the synchronization information.

The method according to the invention further comprises the steps of: separating the AV stream and the data packet from the received signal; Receiving system reference time information from the decoding means of the AV stream; Obtaining a data timestamp from the synchronization metadata included in the data packet; And comparing the data time stamp with the system reference time and performing decoding or reproduction of a data object file at a time point coinciding with each other.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a diagram showing the configuration of a terrestrial DMB broadcast transmission system for synchronizing real-time video and data services according to an embodiment of the present invention.

Referring to FIG. 2, the terrestrial DMB broadcasting transmission system includes an AV signal source 200 for generating audio and video content, a DMB AV encoder 210 for encoding the generated audio and video according to the terrestrial DMB standard, A data server 230 for data service, an ensemble multiplexer 240 for multiplexing the generated AV streams and data packets into one ensemble, a DMB transmitter 250 for OFDM encoding and RF transmission, and the correctness of the devices NTP (Network Time Protocol) server 220 for time synchronization. The data server 230 is a data signal source 231, a data management and control unit 233 for managing and controlling a data signal source and a data encoder, and data for encoding the generated data according to various DMB data transmission / reception standards. The encoder 235 is configured.

When the AV signal source 200 generates video and audio for a video service in DMB broadcasting through real time or a storage medium, the DMB AV encoder 210 uses MPEG-4 and MPEG-2 based terrestrial DMB video matching standards. Encode by At this time, in order to transmit and synchronize timing information of audio and video, time stamps including OCR and CTS in MPEG-4 and PCR and PTS in MPEG-2 are encoded and inserted. In this case, the DMB AV encoder 210 provides a video time stamp (CTS) at the beginning of the program to the data server 230.

For additional data service based on Eureka-147, the data signal source 233 generates Java (JAVA) -based application data and related detailed data such as text, images, and videos through collection and authoring. After the data is stored, they are encoded and broadcast by the data encoder 235 by management and control of the data management and control unit 233. The NTP server 220 also accurately synchronizes the time between the AV signal source 200, the AV encoder 210, and the data server 230.

 The data management and control unit 233 manages the time point at which the data of the data signal source is inserted, the video timestamp (CTS) of the initial program input from the DMB AV encoder, the scene information from the AV signal source known in advance, A time stamp (CTS) based time point is calculated based on the data insertion time using the data insertion time. The calculated synchronization information is transmitted to the data encoder 235, either directly or as meta data for synchronization of video and data.

3A illustrates in detail a method of calculating a time stamp (CTS) based time point at which data is reproduced.

In the case of a recorded broadcast, time information V (b) of a scene into which data synchronized with video is to be inserted can be accurately extracted in advance. In addition, if video data is encoded by the DMB AV encoder 210, each scene can be extracted. A timestamp such as CTS, which is a playback time at the terminal, is inserted into the header of the SL packet .. In a non-streaming type data broadcasting service, a data carousel is stored before the playback time at the terminal. After the broadcast in the form of a), it is downloaded from the terminal and reproduced at a set time point, where the data is a download type application program and related data, and in some cases, may be data previously stored in an inactive memory.

In the present invention, in order to reproduce the data synchronized to a particular scene, the data management and control unit 233 generates the synchronization metadata, and then transmits it using a suitable data protocol.

FIG. 3B is a diagram showing an example of the configuration of the data carousel shown in FIG. 3A, and FIG. 3C is a diagram showing an example of the configuration of the synchronization metadata.

As shown in FIG. 3C, the synchronization metadata may include an identifier, a trigger time (video time stamp), an associated data indicator, data, and the like. The identifier refers to an identifier for distinguishing data, wherein the trigger time corresponds to the decoding, reproduction, and extinction time of the data in the terminal and is calculated in advance based on a pre-calculated video time stamp (CTS). The related data indicator is related to an application program executed in the terminal and indicates data to be reproduced in synchronization with a specific scene, and the data is composed of information that is immediately needed separately from it.

In this case, since the synchronization metadata is inserted before the specific video view point V (b), the trigger time Ts (b) configured in the synchronization metadata should be predicted at the insertion point in advance. This can be calculated by using the video time stamp information (video information / time stamp) of the initial program inputted from the DMB AV encoder 210 and the playback time (V (b)) of the previously known video. Here, video timestamp information at the beginning of the program will be easily extracted since all devices are precisely synchronized in time by the NTP server.

In the case of a simple synchronization data service, as shown in FIG. 3B without requiring synchronization metadata, video time stamp information is inserted directly through a header of a data object repeatedly transmitted to a data carousel, thereby improving the playback time of the data object. You will be able to match the video.

Hereinafter, the synchronization metadata will be described in detail with reference to specific examples.

Synchronization with DMB video service In order to provide data service, trigger time information (trigger time) indicating the time when a specific event in an application is performed is generated to be synchronized with the video service, and then it is generated within a short time from the data server of the sender. Must transmit to terrestrial DMB middleware. That is, after executing an application program in the terminal, in order to perform a specific event synchronized with video, the transmitter should transmit the trigger time and the data to be performed or its indicator from the transmitting side, and triggers a message composed of this information. It is defined as. That is, the trigger packet is an example of the above-described synchronization metadata.

The trigger packet is scheduled and transmitted from the server in advance of the synchronized timing of the trigger so that the application is ready to perform the specific event, and the trigger packet is repeatedly transmitted until the trigger time is reached, so that the application intentions of the event at the time exactly synchronized with the video service are transmitted. To perform certain acts as

In the terrestrial DMB, the TDC packet mode that does not use a low-latency, low-latency data group for the transmission of the trigger packet (see TTAS.KO-07. Let's use. It will also be possible to transmit using other transport protocols.

The format of a trigger packet is shown in Table 1 below.

In [Table 1], “triggertId” is an identifier for identifying a trigger in an application program, “triggerTime” indicates a time point at which an event occurs, and a video timestamp (CTS) at a time point of occurrence of an event for a coordinated service. ). At this time, in order to use the CTS at a specific trigger time, mutual control between the video service equipment and the data server will be required. "privateDataByte" represents data for an application to execute a specific event at the time of trigger. Here, privateDataByte may be composed of the relevant data indicator and data of FIG. 3C.

API Model

Terrestrial DMB middleware defines Trigger interface in dmb.io package defined for receiving DMB data channel to provide synchronized data service. This is an extension of javax.microedition.Datagram (CLDC 1.1 (JSR 139), http://java.sun.com/products/cldc/index.jsp), which is a datagram with event information. Trigger is used to transmit synchronization signal with other media such as A / V. It associates the trigger ID with the visual information to perform the task represented by that trigger.

Even if multiple triggers are received in the broadcasting network, the same ID is treated as the same trigger. When a trigger transmits multiple times, it is intended to indicate a reason for increasing the reception probability and a case in which a trigger refers to a change in time, which may occur due to a discontinuity of the system time clock. However, if the time specified in the trigger has already passed, the trigger is ignored, and the ID of the trigger that has been processed after the specified time has been reused by another trigger.

Once any trigger with the same ID is received, the Trigger object is received as soon as it is received. At this time, doItNow () returns false if the time indicated by the trigger has not yet reached. A trigger with doItNow () set to false is only passed to the application once, even if the trigger is received multiple times with the same ID. However, if the trigger time changes in the middle, a trigger with the same ID may be delivered to the application several times. Finally, when the trigger time runs out or passes, the trigger with doItNow () is passed to the application. In this case, you must immediately perform the action associated with the trigger. After that, even if a trigger with the same ID is delivered, it is treated separately from the trigger that has already returned true in doItNow ().

PrivateData transmitted in Trigger packet is read by using method of Datagram which is upper class of Trigger.

API definition for synchronization service is shown in [Table 2].

4 is a diagram illustrating a configuration of a terrestrial DMB broadcast transmission system for synchronizing real-time video and data services according to another embodiment of the present invention.

FIG. 4 shows a time stamp at the data server 430 when the DMB AV encoder cannot output time information of a video source and video information / time stamp, which is a time stamp information (CTS) of the stream, to the data server in real time. An example of a system using the extractor 437 is shown. Here, the time stamp extractor 437 extracts a time stamp (CTS) of the video from the AV stream output from the DMB AV encoder 410, and the extracted time stamp is input to the data management and control unit 433.

In this case, in order to precompute the time stamp Ts (b) of the data constituted in the synchronization metadata, the encoding delay time of the DMB AV encoder 410 that can be experimentally obtained must be additionally considered.

A more convenient method of synchronized data service will be possible by encoding AV data in advance and storing it in stream form as shown in FIGS. 5 and 6. In this case, the time of video for data insertion and time stamp information at this time can be known in advance.

5 is a diagram showing the configuration of a terrestrial DMB broadcasting transmission system for synchronizing a real-time video and data service according to another embodiment of the present invention.

FIG. 5 illustrates a case where an AV stream is stored as an MPEG-2 TS or a FEC (Forward Error Coding) file thereof.

Referring to FIG. 5, the DMB broadcasting transmission system includes an AV signal source 500, an AV encoder 510 for encoding an AV signal according to a terrestrial DMB standard, and storage means for encoding and storing the AV signal in a stream form ( 560, a data server 530 for generating synchronization metadata for providing a data service synchronized with an AV service using an AV timestamp provided from the storage means, an output signal of the AV encoder and an output of the data server And means (520, 540, 550) for multiplexing and transmitting the signal. Here, the video / data timestamp information indicating the time information of the video into which the data is to be inserted and the timestamp information to be played back is input to the data server 530 in advance, and the data management and control unit 533 uses the data. The synchronization metadata may be generated by determining when to insert the data.

As shown in FIG. 5, while the AV stream is being transmitted by the DMB encoder for general DMB broadcasting, switching of the stream occurs in the switcher when data service is performed. The consideration here is that the switcher performs a re-stamping process, i.e. processing to ensure continuity of time stamps. This is a process of resetting the time stamp pre-inserted into the stream file in the switcher 520 so as to be continuous with the time stamp of the AV stream output from the DMB encoder 510, and a predetermined value is added to the time stamp as a whole. . Therefore, in order to reflect this in the data server 530, the timestamp of the AV stream reset by the switcher 520 and information about a time point at which switching has occurred must be input. Since the reset time stamp is a fixed value shift as a whole, the information needs to be input only at the moment of switching.

6 is a diagram showing the configuration of a terrestrial DMB broadcast transmission system for synchronizing real-time video and data services according to another embodiment of the present invention.

Unlike the system shown in FIG. 5, the transmission system shown in FIG. 6 illustrates a case in which an AV stream is pre-encoded in the form of an MP4 file and then directly inserted into the DMB AV encoder.

When the MP4 file, which is one of the storage file formats, is inserted into the DMB broadcast when the AV stream is encoded in MPEG-4, the M4onM2 processing module 620 packetizes the MPEG-4 SL and the MPEG-2 TS as shown in FIG. You have to go through the process. This process can be performed inside the encoder, but can be developed as a separate device.

When the MP4 file is packetized into MPEG-4 SL and MPEG-2 TS, relative time information in the MP4 is converted into time information such as OCR and CTS. Accordingly, the data server 630 knows in advance the time information of the video into which the data is to be inserted and the video / data timestamp information indicating the time information to be reproduced, and packetizes the MP4 into MPEG-4 SL and MPEG-2 TS. If only the conversion information at the time can be input, it is possible to predict the data time stamp, which is the playback time of the data synchronized with the video.

7 illustrates a receiving system capable of data service synchronized with video according to the present invention.

Referring to FIG. 7, a reception system capable of data service synchronized with video includes an RF reception and channel decoder 710 for receiving a digital multimedia broadcasting signal, demodulating it into a baseband signal, and performing channel decoding, and multiplexing information and service information. MSC processing unit 730 for separating the AV stream and the data packet by means, decoding means 740 for decoding the AV stream, system reference time information and data packet provided from the decoding means 740 for the AV stream. And data reproducing means (760, 770) for providing a data service synchronized with the AV stream using the synchronization metadata contained in the.

The RF reception and channel decoder 710 receives an RF signal, demodulates the baseband signal, decodes the channel, and separates the FIC data and the MSC data. The FIC interpreter 720 interprets the multiplexed information and the service information and provides it to the MSC processor 730, which separates the AV stream and the data packet transmitted through the MSC channel. The AV stream and the data packet are input to the DMB AV decoder 740 and the DMB data decoder 760 and decoded, respectively. The DMB AV playback device 750 and the data playback device 770 play back the AV stream and data in accordance with the playback time, respectively.

In the present invention, the data decoder 760 receives system reference time information such as OCR from the DMB AV decoder 740 and compares it with CTS-based data time stamp information inserted in the header of the synchronization metadata or the data object. At this time, the matching time point is the playing time of the corresponding data object file. Finally, in the data reproducing apparatus 770, after the application indicated by the synchronization metadata is executed, the relevant data indicated by the synchronization metadata and the immediate data inserted into the synchronization metadata are reproduced in accordance with the extracted reproduction time. The data service is synchronized with.

As described above, the method of the present invention may be implemented as a program and stored in a recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.) in a computer-readable form. Since this process can be easily implemented by those skilled in the art will not be described in more detail.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

The present invention as described above, since the data transmitted based on the Eureka-147 can be a service synchronized with the MPEG-4 and MPEG-2 based video services, there is an effect that contributes to the spread of various DMB data broadcasting services.

Claims (23)

A method for providing a data service synchronized with an AV service in digital multimedia broadcasting, Receiving an AV time stamp for the AV data; Calculating a timestamp of the data at the time point at which the data is reproduced in the terminal based on the AV timestamp; Generating synchronization metadata comprising a timestamp of the calculated data; And Encoding and transmitting the synchronization information; and providing a data service synchronized with an AV service in a digital multimedia broadcasting. The method of claim 1, wherein the AV time stamp, A method for providing a video service synchronized data service in a digital multimedia broadcasting, characterized in that it is extracted and provided from an audio / video stream that is encoded and output. The method of claim 1, wherein the AV time stamp, Method for providing a video service synchronized data service in a digital multimedia broadcasting, characterized in that it is provided from a pre-stored AV stream file for the synchronized service. The method of claim 1, wherein the synchronization metadata, And a trigger packet including information for performing an event synchronized with the AV service. The method of claim 4, wherein the trigger packet, A video service in a digital multimedia broadcasting comprising a field for identifying a trigger in a receiving application, a field indicating a point in time at which a corresponding event occurs, and a field indicating a data for execution by an application in a trigger point. Method for providing a synchronized data service. The method as claimed in claim 5, wherein the trigger packet is repeatedly transmitted before a trigger time point. A method for providing a data service synchronized with an AV service in digital multimedia broadcasting, Separating the AV stream and the data packet from the received signal; Receiving system reference time information from the decoding means of the AV stream; Obtaining a data timestamp from the synchronization metadata included in the data packet; And And comparing the data timestamp with the system reference time to execute decoding or playback of a data object file at a matched time point. The method of claim 7, wherein the synchronization metadata, And a trigger packet including information for performing an event synchronized with the AV service. The method of claim 7, wherein the synchronization metadata, And a trigger packet including information for performing an event synchronized with the AV service. The method of claim 9, wherein the trigger packet, And a field for identifying a trigger in a receiving application, a field for recording a trigger time, which is a point in time at which the corresponding event occurs, and a field for indicating data for execution by the application in a trigger point. Video service in broadcast A method for providing a synchronized data service. 10. The method of claim 9, wherein the trigger packet transmits a false signal to a receiving application if the trigger packet is to be notified before a specific event occurs, and receives a true signal if data must be processed immediately in response to the event. A video service synchronized data service in a digital multimedia broadcasting characterized in that delivered to the application on the side. An apparatus for providing a data service synchronized with an AV service in digital multimedia broadcasting, An AV encoder for encoding an AV signal according to the terrestrial DMB standard and providing an AV timestamp to the data server; A data server for generating synchronization metadata for providing a data service synchronized with an AV service using the AV timestamp; A time synchronization server for accurate time synchronization of the AV encoder and the data server; And And means for multiplexing and transmitting the output signal of the AV encoder and the output signal of the data server. The method of claim 12, wherein the data server, A data signal source for generating various data related to digital multimedia broadcasting; The data management and control unit for calculating a timestamp of data at the time point at which data is reproduced in the terminal based on the AV timestamp, and generating synchronization metadata including the timestamp of the calculated data; Apparatus for providing a data service synchronized with the AV service in a digital multimedia broadcasting, characterized in that it comprises a data encoder for generating a data packet by encoding the various data for the data service and the synchronization metadata. The method of claim 12, wherein the synchronization metadata, Apparatus for providing a video service synchronized data service in a digital multimedia broadcasting, characterized in that the trigger packet consisting of information for performing an event synchronized with the AV service. The method of claim 14, wherein the trigger packet, A video service in a digital multimedia broadcasting comprising a field for identifying a trigger in a receiving application, a field indicating a point in time at which a corresponding event occurs, and a field indicating a data for execution by an application in a trigger point. Device for providing a synchronized data service. 15. The apparatus of claim 14, wherein the trigger packet is repeatedly transmitted before a trigger time point. An apparatus for providing a data service synchronized with an AV service in digital multimedia broadcasting, An AV encoder for encoding the AV signal according to the terrestrial DMB standard; Storage means for encoding and storing the AV signal in a stream form; A data server for generating synchronization metadata for providing a data service synchronized with an AV service using an AV timestamp provided from the storage means; And And means for multiplexing and transmitting the output signal of the AV encoder and the output signal of the data server. The method of claim 17, wherein the synchronization metadata is And a trigger packet including information for performing an event synchronized with the AV service. The method of claim 18, wherein the trigger packet, A video service in a digital multimedia broadcasting comprising a field for identifying a trigger in a receiving application, a field indicating a point in time at which a corresponding event occurs, and a field indicating a data for execution by an application in a trigger point. Device for providing a synchronized data service. An apparatus for providing a user with a data service synchronized with an AV service in a digital multimedia broadcasting, An RF receiving and channel decoder for receiving a digital multimedia broadcasting signal, demodulating the baseband signal, and performing channel decoding; An MSC processing unit for separating the AV stream and the data packet by the multiplexing information and the service information; AV stream decoding means for decoding the AV stream; And AV service in a digital multimedia broadcasting including data reproducing means for providing a data service synchronized with the AV stream by using system reference time information provided from the decoding means of the AV stream and synchronization metadata included in the data packet. A device for providing a data service synchronized with a user. The method of claim 20, wherein the synchronization metadata, Apparatus for providing a video service synchronized data service to a user in a digital multimedia broadcasting, characterized in that the trigger packet consisting of information for performing an event synchronized with the AV service. The method of claim 21, wherein the trigger packet, And a field for identifying a trigger in a receiving application, a field for recording a trigger time, which is a point in time at which the corresponding event occurs, and a field for indicating data for execution by the application in a trigger point. Apparatus for providing a video service synchronized data service to a user in a broadcast. 22. The method of claim 21, wherein the trigger packet transmits a false signal to a receiving application if the trigger packet is to be notified before a specific event occurs, and receives a true signal if data must be processed immediately in response to the event. Apparatus for providing a video service synchronized data service to a user in a digital multimedia broadcasting, characterized in that delivered to the application on the side.

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