JP5466633B2 - Stream switching method and digital broadcast transmission system - Google Patents

Description

  The present invention relates to a stream switching method and a technology of a digital broadcast transmission system.

Digital broadcasting has been started in Japan since 2003, and various stream switching techniques have been disclosed in order to easily realize digital broadcasting program organization.
A digital broadcast transmission apparatus (hereinafter referred to as a transmission apparatus) that encodes an input signal, performs multiplexing / remultiplexing, and transmits a broadcast transport stream (hereinafter referred to as a broadcast TS (Transport Stream)) to the transmission apparatus. Document 1 discloses a bit stream switching system that selectively transmits a plurality of streams without interruption by synchronizing the phases of the plurality of streams at the time of encoding. Patent Document 2 discloses a system switching system that seamlessly switches systems in a duplexed system by synchronizing input signals to an encoding unit.
These switching systems are systems that realize switching at a baseband level (analog signal) such as an NTSC (National Television System Committee) signal.

Japanese Patent Laid-Open No. 2001-145022 JP 2000-269864 A

  By the way, the material constituting the broadcast program of digital broadcasting includes live material that is encoded online, and stored material that is encoded offline in advance and stored in the MPEG (Motion Picture Experts Group) -2 TS format in the transmission apparatus. There is. FIG. 7 shows a system in which a program is configured by switching between these live materials and stored materials at an arbitrary timing using the above two disclosed technologies.

In other words, the content distribution server 710 once reproduces the stored material (stored program, content) by the reverse encoding unit 711, converts it to the baseband level (NTSC signal), and then outputs the stream to the transmission device 720. . The sending device 720 encodes the storage material input from the content distribution server 710 with the encoding unit 725, and encodes the live material input from another system with the encoding unit 724 with the external synchronization clock 730. The phases of the streams output from the units 724 and 725 are synchronized, and the switcher 721 switches according to the external synchronization clock 730.
The switched stream is multiplexed by the multiplexing unit 722, remultiplexed by the remultiplexing unit 723, and transmitted as a broadcast TS.

  In such a switching system, not only is it unavoidable that the quality of content is deteriorated due to repeated encoding and inverse encoding of the stored material, but also the encoding of the inverse encoding unit 711 and the transmission device 720 of the content distribution server 710. Complex synchronization processing of the units 724 and 725 and the switcher 721 is required.

  The present invention has been made in view of such a background, and an object of the present invention is to switch contents by a simple method in digital broadcasting.

In order to solve the above-mentioned problems, the present invention provides a digital broadcasting device that switches a plurality of streams to send digital broadcast content, and sends the content to the transmission device in the form of an IP (Internet Protocol) packet . a stream switching method in a digital broadcasting carried out in a content distribution server which transmits, the content delivery server, the delivery device has finished sending the transmission start time and the content is a time for starting the delivery of the content A transmission end time that is a time is acquired from the transmission device, a selection input for selecting an I frame that is a still image component for each predetermined time of a moving image of the content is received, and based on the selection input, The content switching time indicating the switching time is determined and is switched from the sending device. When receiving the notice of the processing start, sends said content switch time to the delivery device, and transmits the data of the content to the sending device in accordance with the transmission start time and the transmission end time, the delivery device, the delivery A start time and a transmission end time are transmitted to the content distribution server, a notification of the switching process start is transmitted to the content distribution server at a time set in advance of the transmission start time, and the content Receiving the content switching time and the data of the content to be switched from the distribution server, and switching the stream from the currently transmitted content to the content received from the content distribution server at the content switching time , To do.
Other solutions will be described as appropriate in the embodiments.

  According to the present invention, contents can be switched by a simple method in digital broadcasting.

It is a figure which shows the structural example of the digital broadcast transmission system which concerns on this embodiment. It is a figure which shows the example of the time information registration screen which concerns on this embodiment. It is a figure which shows the example of the content switching time registration screen which concerns on this embodiment. It is a flowchart which shows the flow of the content transmission process which concerns on this embodiment. It is a flowchart which shows the detailed procedure of the content switching process which concerns on this embodiment. It is a figure for demonstrating the determination method of switching PTS which concerns on this embodiment. It is a figure which shows the structural example of the conventional digital broadcast transmission system.

Next, modes for carrying out the present invention (referred to as “embodiments”) will be described in detail with reference to the drawings as appropriate.
In this embodiment, a case where one program is broadcast will be described as an example. However, the present invention is not limited to this, and each program can be transmitted even when an arbitrary number of programs (for example, two or three) are multiplexed and transmitted. The present invention can be applied every time.

(System configuration)
FIG. 1 is a diagram illustrating a configuration example of a digital broadcast transmission system according to the present embodiment.
The digital broadcast transmission system 10 includes a transmission device 2 that switches and transmits a plurality of input TSs at the MPEG-2 TS level, and a content distribution server 1 that distributes accumulated content (stored material).
In the present embodiment, each program (content) is composed of audio, video, and data, and the program information is recorded in PSI / SI (Program Specific Information / Service Information).

The content distribution server 1 transmits the content in the form of a TS stream (hereinafter referred to as a stream), and the transmission device 2 further transmits the content in a broadcast TS format to an OFDM (Orthogonal Frequency Division Multiplex) modulator (not shown). Send it out.
The stream is sent in units of TS packets (hereinafter referred to as packets). The packet includes a PCR (Program Clock Reference) that is a reference time for synchronizing a reproduction time in a receiving device (not shown), and a PTS (Presentaiotion Time Stamp) that is information related to a time for reproducing and displaying data stored in the packet. ). The PCR is given based on the time of the internal clock of the sending device 2.
The receiving device has an STC (System Time Clock) that is an internal clock synchronized with the PCR, and reproduces and displays the data held in this packet when the time stamped by the STC becomes equal to the PTS.

(Content distribution server)
The content distribution server 1 includes a distribution control unit 101, a content acquisition unit 102, a content distribution unit 103, a storage unit 104, an input unit 105, a display unit 106, a time information registration unit 107, and a communication unit 108.
The distribution control unit 101 controls the units 102 to 108.
The content acquisition unit 102 acquires content from the storage unit 104 according to the time information registered by the time information registration unit 107 and stored in the storage unit 104.
The content distribution unit 103 registers the content acquired by the content acquisition unit 102 in accordance with the time information registered by the time information registration unit 107 and stored in the storage unit 104 according to the format of the content, using RTP (Real-time Transport Protocol). The data is distributed to the switcher 202 of the transmission apparatus 2 in the form of Mpeg-2 TS via the cable 301 or an ASI (Asynchronous Serial Interface) cable 302. When transmitting Mpeg-2 TS via the RTP cable 301, it is converted into RTP format and transmitted via the Internet or a dedicated line.

The input unit 105 is an input interface such as a keyboard and a mouse.
The display unit 106 is an output interface such as a display.
The time information registration unit 107 acquires schedule information such as an output format, a transmission start time, and a transmission time end time from the scheduler, or time information such as a content switching time that is a time when the content is switched to the scheduler 207 of the transmission device 2. Or send. The output format, transmission start time, transmission time end time, and content switching time will be described later.
The communication unit 108 transmits / receives information to / from the sending device 2. Also, the storage unit 104 stores content and time information registered via a screen described later in FIG. 2 or FIG.

(Sending device)

The transmission apparatus 2 includes a control unit 201, a switcher 202, a multiplexing unit 203, a remultiplexing unit 204, a TS transmission unit 205, a PCR generation unit 206, a scheduler 207, a communication unit 208, an encoding unit 209, and a content storage unit 210. Have.
The control unit 201 controls the scheduler 207, the communication unit 208, and the switcher 202 in order to perform content (stream) switching processing.
The switcher 202 switches streams according to schedule information sent from the scheduler 207. Specifically, the content input in the MPEG-2 TS format input from the encoding unit 209, the content distribution unit 103 of the content distribution server 1, and the content storage unit 210 is switched at the transmission start time acquired from the scheduler 207. To the multiplexing unit 203. However, the time information acquired from the time information registration unit 107 of the content distribution server 1 is used when switching to the content input in the MPEG-2 TS format from the content distribution unit 103.

The multiplexing unit 203 multiplexes the TS (stream) acquired by the switcher 202 and outputs it in the MPEG-2 TS format. More specifically, the multiplexing unit 203 multiplexes the audio TS and video TS input from the switcher 202 and a DSMCC (Digital Storage Media Command and Control) section TS prepared for data broadcasting separately from this, and MPEG -2 Outputs to the remultiplexing unit 204 in the TS format.
The remultiplexing unit 204 multiplexes the PSI / SI information into the MPEG-2 TS output from the multiplexing unit 203 and converts it into a broadcast TS format that conforms to the ISDB-T standard.
The TS transmission unit 205 outputs the broadcast TS input from the remultiplexing unit 204 from the TS board in the TS transmission unit 205 to an OFDM modulation unit (not shown). The OFDM modulation unit OFDM modulates the broadcast TS input from the TS transmission unit 205 and transmits it as a broadcast wave.

The PCR generation unit 206 generates a PCR added to the broadcast TS according to the internal clock.
The scheduler 207 manages schedule information such as the switching timing (transmission start time) of the broadcast TS in the switcher 202, and transmits a switching notification to the switcher 202 a predetermined time before the transmission start time. In addition, a switching process start notification or the like is transmitted to the time information registration unit 107 via the communication unit 208.
The encoding unit 209 captures and encodes an input video and input audio such as a live material input from the outside via an ASI cable 303 from the outside, for example, an NTSC signal, and encodes it into a TS format used for MPEG-2 TS. Packetize. That is, the encoding unit 209 encodes the input audio into, for example, an AAC (Advanced Audio Coding) format, further converts it into a TS format, and outputs it to the switcher 202. Also, the encoding unit 209 converts the video input with the NTSC signal via the ASI cable 303 into, for example, H.264. The data is encoded into the H.264 format, further converted into the TS format, and output to the switcher 202.

  The content storage unit 210 stores content (accumulated material) that has been encoded offline in advance and saved as a file in the MPEG-2 TS format. The content stored in the content storage unit 210 can be freely read by the switcher 202.

  The content distribution server 1 and the transmission device 2 are realized by a PC (Personal Computer) or the like, and the units 101 to 103 and 107 of the content distribution server 1 and the units 201 to 207 and 209 of the transmission device 2 are not shown in ROM (Read). A program stored in a Only Memory (HDD) or a Hard Disk Drive (HDD) is developed in a RAM (Random Access Memory) and executed by a CPU (Central Processing Unit).

(Time information registration screen)
2 and 3 explain the screen at the time information registration performed in step S101 described later in FIG. 2 and 3 are screens displayed on the display unit 106 of the content distribution server 1. FIG.
FIG. 2 is a diagram illustrating an example of a time information registration screen according to the present embodiment.
The time information registration screen 350 includes a time information registration table 351, a change button 352, and a registration button 353.
The time information registration table 351 has an output format, a transmission start time, a transmission end time, a content name, and a content switching time.
Among these, the output format, the transmission start time, and the transmission end time are schedule information acquired from the scheduler 207 of the transmission apparatus 2 by the time information registration unit 107.

The output format is a communication method for distributing a stream (TS) from the content distribution server 1 to the transmission device 2.
The transmission start time and the transmission end time are a start time and an end time at which the transmission device 2 transmits the content.
The content name stores the path to the content to be distributed and the file name of the content.
The content switching time indicates the time in the content when the switcher 202 switches to the target content at the transmission time. Here, the above-described transmission start time and transmission end time indicate the time in Japan standard time, whereas the content switching time is a time when the time at which the content is started is “0”.

In the example shown in FIG. 2, the information input to the first record is “ASI”, and “ContentA” from 18:00 on June 30, 2010 to 18:15 on June 30, 2010. "Is sent out (broadcast) from the sending device 2. The data sent in 15 minutes is data for 15 minutes from the time when 2 minutes and 30 seconds have passed since the start of “Content A”.
In the record whose output format is “RTP”, the content name and content switching time are blank, indicating that these pieces of information are not yet registered.

  When the user selects and inputs the change button 352, the contents of the time information registration table 351 can be changed. When the user selects and inputs the registration button 353, the contents of the time information registration table 351 are stored in the storage unit 104 as time information.

FIG. 3 is a diagram illustrating an example of a content switching time registration screen according to the present embodiment.
The content switching time registration screen 400 has a file name designation window 401, a video display area 402, a frame display area 403, a registration button 405, a return button 406, a reference button 407, and a move button 408. Yes.

The file name designation window 401 is a window for displaying the file name, path, and link of the content to be registered as the content switching time. The user directly inputs the content via the input unit 105 or presses the reference button 407. Specify the content by selecting from the pull-down menu that is displayed when the selection is entered.
In the video display area 402, the video (still image) of the I frame selected in the frame display area 403 is displayed in the content specified in the file name specification window 401. Here, the I frame is a still image component at every predetermined time when the moving image is divided at every predetermined time.
The frame display area 403 displays a time bar related to the content to be processed. That is, reference numeral 413 indicates the start of content, and reference numeral 414 indicates the end of content. The time bar is divided for each I frame, and when the user selects a frame in the time bar (reference numeral 411), a still image of the corresponding I frame is displayed in the video display area 402.
Further, from the I frame, an interval between frames corresponding to the transmission time calculated from the transmission start time and the transmission end time in FIG. 2 is highlighted (reference numeral 412).
The designated I frame 411 can be moved in I frame intervals by selecting and inputting the move button 408. Incidentally, the I frame interval is about 2 seconds in the one-segment broadcasting.

In FIG. 3, the information of the content regarding the record whose output format in FIG. 2 is “ASI” is displayed. Accordingly, since the transmission time calculated from the transmission start time and the transmission end time in FIG. 2 is 15 minutes, an interframe interval 412 corresponding to 15 minutes from the I frame 411 is highlighted.
When the user selects and inputs the registration button 405, the contents of FIG. 3 are reflected in the time information registration table 351 of FIG. That is, the file name (link or path) displayed in the file name designation window 401 is reflected in the content name in FIG. 2, and the time of the I frame 411 in FIG. 3 is reflected in the content switching time in FIG.
When the user selects and inputs the return button 406, the information returns to before the change.

  By registering such time information, preparation for switching at the I frame is made at the transmission start time. In this example, starting a switching target stream from an I frame is a necessary condition for seamless switching of MPEG-2 TS.

(processing)
FIG. 4 is a flowchart showing the flow of content transmission processing according to the present embodiment. From now on, when describing it as a single program, it will be described separately from the stream when describing it as a content, and when describing it as a flow of information.
First, the user inputs schedule information such as the output format, the transmission start time, and the transmission end time in FIG. 2 to the scheduler 207 of the transmission apparatus 2 from an input unit (not shown) of the transmission apparatus 2. The scheduler 207 transmits the input schedule information to the content distribution server 1.
The time information registration unit 107 of the content distribution server 1 that has received an instruction to start time information registration from the user displays the time information registration screen shown in FIG. 2 including the schedule information received from the scheduler 207 and the switching scene selection screen shown in FIG. The information is displayed on the display unit 106, and the user registers time information such as the content switching time via the input unit 105 (S101).
Here, the time information is information including the output format, the transmission start time, the transmission end time, the content name, and the content switching time in FIG.
Next, the scheduler 207 determines whether or not the current time is the switching preparation start time by comparing the current time indicated by a timer (not shown) with the switching scene time (S102). The switching preparation start time is a time that is a predetermined time before the transmission start time in FIG.
As a result of step S102, when the current time is not the switching preparation start time (S102 → No), the scheduler 207 returns the process to step S102.

As a result of step S102, when the current time is the switching preparation start time (S102 → Yes), the scheduler 207 notifies the switcher 202 of the start of the switching process and also starts the switching process to the distribution control unit 101 of the content distribution server 1. Notification is made (S103).
Next, the distribution control unit 101 notifies the control unit 201 of the sending apparatus 2 of the content switching time of the target content (S104).
Receiving the content switching time, the control unit 201 prepares to receive content, and when the reception preparation is completed, notifies the distribution control unit 101 of the content distribution server 1 of the completion of content reception preparation (S105).
Then, the distribution control unit 101 causes the content acquisition unit 102 to acquire content according to the time information registered in the storage unit 104 (information registered in FIG. 2), and causes the content distribution unit 103 to distribute the content to the switcher 202. (S106). For example, the content distribution unit 103 distributes the content of “Content A” to the switcher 202 via the ASI cable 302 from the content switching time 2 minutes 30 seconds before (2 minutes 29 seconds, etc.) in the Mpeg-2 TS format. To do.
When content distribution starts, the control unit 201 performs content switching processing (S107). The content switching process will be described later with reference to FIG.

When the content switching process is completed, the switcher 202 notifies the content distribution server 1 of the switching completion (S108), and the content distribution server 1 notifies the sending apparatus 2 of the switching process end notification (S109). finish.
The control unit 201 determines whether or not the sending apparatus 2 has finished sending the broadcast TS (S110).
If the result of step S110 is that transmission of the broadcast TS has not been completed (S110 → No), the control unit 201 returns the process to step S102.
If the result of step S110 is that the broadcast TS has been sent out (S110 → Yes), the control unit 201 ends the process.

(Content switching process)
FIG. 5 is a flowchart showing a detailed procedure of the content switching process (step S107 in FIG. 4) according to the present embodiment. Here, a case will be described in which a stream is switched from a switched stream to a switched stream.
First, the control unit 201 stores the switching target stream and the switching target stream in a buffer (S201). As a result, the switcher 202 temporarily interrupts the output of the switched stream that has been output to the multiplexing unit 203.
Next, the control unit 201 determines a switching PTS that is a PTS at the time of switching in the switching target stream and the switching target stream from the PCR at the current time (S202).

Here, the determination of the switching PTS in step S202 will be described with reference to FIG.
In FIG. 6, the vertical axis indicates the time given to the packet, and the horizontal axis indicates the order of TS packets.
A line 611 in FIG. 6 indicates the PCR of the stream output from the TS transmission unit 205, and a line 612 indicates the PTS of the encoded stream output from the TS transmission unit 205. The line 612 is wavy up and down because the amount of data per time in the encoded stream is different. A line 613 is a line when the line 611 is translated in the time direction by the difference between the initial values of PTS and PCR.
In step S103, the value of the PCR generated by PCR generation unit 206 to the switching _{T 1} second before is assumed to be a switch _{T 1} second before PCR601, the value of the PCR in the content switching time _{T 1} seconds ₁ second before switching _T It becomes the time of the later switching point PCR602.
Then, the control unit 201 sets a PTS that is translated in the time direction by the difference between the initial values of the PTS and the PCR from the time of the switching point PCR602 as a switching PTS603. That is, the control unit 201 sets the PTS obtained by adding the difference between the initial value of the PTS time and the initial value of the PCR time to the time of the switching point PCR 602 as the switching PTS 603.

Returning to the description of FIG. 5, the control unit 201 obtains the difference between the PTS corresponding to the content switching time notified in step S <b> 104 in FIG. 5 (hereinafter referred to as switching content PTS) and the switching PTS determined in step S <b> 202. The stream time correction value (hereinafter, stream time correction value) as the PTS correction value is calculated (S203).
Subsequently, the control unit 201 deletes the stream having the PTS before the switching content PTS among the switching target streams stored in the buffer (S204). Thereby, the switching target stream is cued in the switching scene (I frame 411 in FIG. 3) registered in step S101.

Next, the control unit 201 corrects the PTS in each packet of the switching target stream stored in the buffer using the stream time correction value (S205). Specifically, the control unit 201 adds the stream time correction value to each PTS of a packet having a PTS after the switching PTS. As a result, the PTS in each packet of the switching target stream can be synchronized with the PCR managed by the sending apparatus 2. This is because the PTS of the switching target stream at the stage of transmission from the content distribution server 1 is not necessarily a value synchronized with the PCR managed by the transmission device 2. On the receiving device side (not shown), the stream is played back assuming that the PTS conforms to the PCR. Therefore, if the stream to be switched is sent to the receiving device without performing step S205, playback on the receiving device becomes impossible.
Then, the control unit 201 multiplexes the switching target stream stored in the buffer to the switcher 202 before the switching PTS (packet having a PTS corresponding to the switching PTS). Are sequentially output (S206).
When the PTS in the switching target stream becomes the switching PTS, the control unit 201 causes the switcher 202 to sequentially output the switching target stream stored in the buffer to the multiplexing unit 203 (S207).

  In step S205, by correcting the PTS of the switching target stream, the PTS of the stream before and after switching takes a continuous value, and the start of the switching target stream starts from the I frame. As a result, the streams are seamlessly switched and played back when viewed on the receiving device. In addition, the I frame that is the start of the switching target stream is a switching scene that has been designated in advance.

(Summary)

According to the present embodiment, when a service that configures one broadcast program by switching a plurality of input system streams based on stored material and live material is realized by the system of the content distribution server 1 and the transmission device 2, The scene where the content distributed from the content distribution server 1 starts (hereinafter referred to as switching scene) can be controlled with a simple configuration.
That is, according to the present embodiment, the time information (content switching time) held by the content itself stored in the content distribution server 1 and the time information (transmission start time) managed on the transmission device 2 side are included. By exchanging between the content distribution server 1 and the sending device 2, switching by the switcher can be performed even if a means such as an IP packet in which the arrival time of the stream is not guaranteed is used.
In addition, since the digital signal can be transmitted as it is from the content distribution server 1 to the transmission device 2, the digital signal is reverse-encoded into an NTSC signal (analog signal) by the content distribution server and then encoded by the transmission device. Since the process of returning to the content is unnecessary, it is possible to prevent the quality of the content from being lowered.
Further, since the time information of the digital signal is used, it is not necessary to synchronize the NTSC signal.

DESCRIPTION OF SYMBOLS 1 Content delivery server 2 Sending apparatus 101 Delivery control part 102 Content acquisition part 103 Content delivery part 104 Storage part 105 Input part 106 Display part 107 Time information registration part 201 Control part 202 Switcher 203 Multiplexing part 204 Remultiplexing part 205 TS transmission Unit 206 PCR generation unit 207 scheduler 209 encoding unit 210 content storage unit

Claims (4)

Stream switching method in digital broadcasting performed by a transmission device that switches a plurality of streams to transmit digital broadcast content and a content distribution server that transmits the content to the transmission device in the form of an IP (Internet Protocol) packet Because
The content distribution server is
Get the transmission end time is the time to end the transmission of the time a transmission start time and the content is that the delivery device starts transmission of the content from the delivery device, stationary at predetermined time moving image of the content When a selection input for selecting an I frame that is an image component is received, a content switching time indicating a switching time in the content is determined based on the selection input, and a notification of switching processing start is received from the sending device , Transmitting the content switching time to the sending device, sending the content data to the sending device according to the sending start time and the sending end time ,
The sending device is
The transmission start time and the transmission end time are transmitted to the content distribution server, the notification of the switching process start is transmitted to the content distribution server at a predetermined time before the transmission start time, Receiving the content switching time and the data of the content to be switched from the content distribution server, and switching the stream from the currently transmitted content to the content received from the content distribution server at the content switching time;
And a stream switching method. The content distribution server is
When sending the content data to the sending device,
Stream switching method according to claim 1, characterized by transmitting from the predetermined time before the content switching time data of the content to the sending device. The content data is transmitted from the content distribution server to the sending device in the form of a packet,
The packet is managed by PCR, which is a reference time for synchronizing the reproduction time in the receiving device, and is given a PTS which is information about the time for reproducing and displaying the data stored in the packet,
The sending device is
When generating the PCR and sending information to the receiving device, the PCR is attached to the information sent to the receiving device,
For the PCR corresponding to the content switching time, a PTS obtained by adding a difference between the initial value of the time in the PCR and the initial value of the time in the PTS is set as a switching PTS,
Calculating a PTS correction value which is a difference between the PTS corresponding to the content switching time and the switching PTS;
A packet having a PTS before the switching PTS is deleted from the content data;
The stream switching method according to claim 2, wherein the PTS correction value is added to each PTS of a packet having a PTS after the switching PTS. In digital broadcasting, a digital broadcasting transmission system for switching a plurality of streams and transmitting the contents of the digital broadcasting,
A storage unit for storing the content;
Get the transmission end time is the time to end the transmission of the time a transmission start time and the content is that the delivery device starts transmission of the content from the delivery device, stationary at predetermined time moving image of the content A time information registration unit that receives a selection input for selecting an I-frame that is an image component and determines a content switching time indicating a switching time in the content based on the selection input;
A delivery control unit for transmitting the content switching time to the sending device when a notification of switching processing start is received from the sending device;
A content distribution unit that transmits the data of the content in the form of an IP packet to the transmission device according to the transmission start time and the transmission end time ;
A content distribution server comprising:
A scheduler for transmitting the transmission start time and the transmission end time to the content distribution server, and transmitting the notification of the switching process start to the content distribution server at a predetermined time before the transmission start time. When,
A control unit that receives the content switching time and the content data to be switched from the content distribution server, and switches the stream of the currently transmitted content to the content received from the content distribution server at the content switching time ; ,
A delivery device comprising:
A digital broadcast transmission system comprising:

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