EP3175623A1

EP3175623A1 - Method for broadcasting an alert service

Info

Publication number: EP3175623A1
Application number: EP15753622.8A
Authority: EP
Inventors: Ludovic Poulain; Laurent Roul
Original assignee: Enensys Technologies SA
Current assignee: Enensys Technologies SA
Priority date: 2014-07-31
Filing date: 2015-07-30
Publication date: 2017-06-07
Also published as: RU2017105010A; RU2017105010A3; WO2016016403A1; FR3024626B1; RU2691101C2; US20170188117A1; FR3024626A1; US10321205B2

Abstract

The present invention concerns a method for broadcasting an alert service in a system for broadcasting audiovisual digital programmes in a single-frequency network. The method comprises the steps, carried out by a module for inserting the alert service, of: - obtaining (E301, E301, E302) transmission frames comprising the alert service and other services, - associating (E303) a marker with each transmission frame, - identifying (E303, E305) the identifiers of the packets of audio and video components of the alert service and of the packets of audio and video components of the other services, - receiving a command to broadcast an alert message, - storing the video and audio packets of the alert service from the first transmission frame marker following receipt of the command to broadcast an alert message, - replacing, from the second transmission frame marker following receipt of the command to broadcast an alert message, all of the packets of the video and audio components of the services other than the alert service with the packets of the alert service stored in the backup memory and replacing the identifiers of packets of audio and video components of the alert service respectively with the identifiers of packets of the audio or video component of the replaced packet in order to form a new transmission frame.

Description

Method for broadcasting an alert service

The present invention relates to the field of broadcasting an alert service in a system for broadcasting digital audiovisual programs within a single frequency plate.

In audiovisual digital program broadcasting systems, the audiovisual data streams are multiplexed and time-tagged to allow SFN (Single Frequency Network) transmission of these.

SFN (Single Frequency Network) broadcasting is characterized in that the broadcasting of the services is carried out by the transmission of the same data stream by different transmitters on one and the same modulation frequency. Therefore, it is necessary that these different transmitters receive exactly the same content and are finely synchronized with each other to avoid generating interference in the places at the junction of the coverage areas of different transmitters.

This synchronization between the different SFN transmitters can, for example, be achieved by inserting in the stream distributed to these transmitters synchronization such as the T2-MI timestamp (T2-Modulator Interface) packets in English which correspond in the DVB-T2 standard to the time labels, and MIP for (Mega-frame Initialization Packet in English) used in the DVB-H and DVB standards -T. This mechanism is described in the document: "Digital Video Broadcasting (DVB); DVB mega-frame for Single Frequency Network (SFN) synchronization Modulator Interface (T2-MI) for a second generation digital terrestrial television broadcasting system (DVB-T2) of the ETSI (European Telecommunications Standards Institute) under the reference ETSI TS 102 773 VI .1.1 (2009-09). The transmitting point receiving the stream then synchronizes to the received stream, for example using these T2-MI packets of the DVB-T2 timestamp type. We call this synchronization of the point of emission on the received stream causing the synchronization between them of all the points of emission, the SFN synchronization of the point of emission.

SFN diffusion is characterized by the definition of SFN plates. An SFN plate is a geographical area covered by a set of transmitters whose number is greater than or equal to one. These transmitters are finely synchronized and emit exactly the same data stream on the same frequency.

In some areas, people are subject to major hazards such as volcanic eruptions, hurricanes, typhoons. In order to allow these populations to take precautions before the arrival of such events, warning messages are broadcast by the authorities. The broadcasting of such alert messages via a broadcasting system of digital audiovisual programs SFN is an interesting solution but difficult to implement by the synchronization of different SFN transmitters and the multiplexing of audiovisual streams.

The present invention aims at enabling a broadcasting system for audiovisual digital programs within a single frequency plate to be able to broadcast an alert service in a simple, fast and not very complex way to implement.

The invention relates to a method for broadcasting an alert service in a system for broadcasting audiovisual digital programs within a single-frequency plate, characterized in that the method comprises the steps performed by an insertion module of the alert service:

obtaining frames comprising the alert service and other services,

- association of a mark for each frame, identification of the identifiers of the audio and video component packets of the alert service,

- identifying the identifiers of the audio and video component packets of the other services,

receiving a command for broadcasting an alert message,

storing the video and audio packets of the alert service from the first frame mark following receipt of the command to broadcast an alert message,

replacing, from the second frame mark following the reception of the broadcast command of an alert message, all the video and audio component packets of the other services that the service packet alert service. alert stored in the backup memory and replacing the audio and video component packet identifiers of the alert service respectively by the packet identifiers of the audio or video component of the replaced packet to form a new frame.

The invention also relates to a device for broadcasting an alert service in a system for broadcasting audiovisual digital programs within a single-frequency plate, characterized in that the device comprises:

means for obtaining frames comprising the alert service and other services,

means for associating a mark for each frame,

means for identifying the identifiers of the audio and video component packets of the alert service,

means for identifying the identifiers of the audio and video component packets of the other services,

means for receiving a command for broadcasting an alert message,

means for storing the video and audio packets of the alert service from the first frame mark following receipt of the command to broadcast an alert message,

means for replacing, from the second frame mark following reception of the broadcast command of an alert message, all the video and audio component packets of the other services that the alert service by the alert service packets stored in the backup memory and replacing the audio and video component packet identifiers of the service respectively by the packet identifiers of the audio or video component of the replaced packet to form a new frame.

Thus, the system for broadcasting audiovisual digital programs within a single-frequency plate can broadcast an alert service in a simple, fast and not very complex to implement.

Indeed, the present invention is able to broadcast the alert service less than two frames after receiving a command to broadcast an alert message.

According to one particular embodiment of the invention, the replacement of all the packets of the video and audio components of the services other than the alert service by the alert service packets stored in the backup memory is broken down into sub-steps. from:

replacing, from the second frame mark following the reception of the broadcast command of an alert message, all the packets of the video and audio components of the other services that the alert service by null packets,

replacement of the null packets by the alert service packets stored in the backup memory.

Thus, alert service packets do not need to be stored as many times as other services exist.

According to one particular embodiment of the invention, the frames are T2-type frames and the method further comprises the step of encapsulating the packets of the new frame in a T2-MI stream.

Thus, the present invention is applicable in new generation broadcast systems.

According to a particular embodiment of the invention, the T2 frames comprising the alerting service and the other services are included in at least one T2-MI stream and obtaining the T2 frames is performed by de-encapsulating the T2 frames of the stream T2-MI.

Thus, the present invention is applicable in new generation broadcast systems.

According to a particular embodiment of the invention, the T2 frames comprising the alert service and the other services are included in a single T2-MI stream.

Thus, the architecture of the broadcasting system is simplified. According to a particular embodiment of the invention, the T2 frames comprising the alert service and the other services are included in two T2-MI streams, the frames of the alert service being encapsulated in a T2-MI stream different from the T2-MI stream. T2-MI stream in which the T2 frames comprising the other services and the method comprises the step of aligning the frames of the alert service and the frames of the other services.

Thus, by encapsulating the frames of the alert service in another T2-MI stream, it is possible to have a generation of the centralized alerting service, for example, by an organization, such as a state, in parallel with the classical operators of diffusion.

According to a particular embodiment of the invention, the T2 frames are included in TS streams and the method further comprises the steps of:

calculating the ratio between the number of video and audio component packets of the alert service and the number of video component packets of the alert service and the other services,

determination of time tagging for each TS stream.

Thus, the new frames conform to the standard used for broadcasting.

According to a particular embodiment of the invention, the method furthermore comprises the step of receiving a stop command for broadcasting an alert message and the packets of the other services are not replaced from the mark of the frame following the reception of the command to stop broadcasting an alert message.

The characteristics of the invention mentioned above, as well as others, will appear more clearly on reading the following description of an exemplary embodiment, said description being given in relation to the attached drawings, among which:

FIG. 1 illustrates an exemplary architecture for broadcasting an alert service in an audiovisual digital program broadcasting system within a single-frequency plate according to the present invention;

FIG. 2 represents an insertion module of an alert service for a synchronous terrestrial broadcast within a single-frequency plate according to the present invention;

Figs. 3 represent an example of an algorithm for synchronous terrestrial broadcasting within a single-frequency plate according to the present invention;

FIG. 4 shows an example of a T2-MI stream received and processed according to the present invention; FIG. 5 represents the reception of a command for broadcasting an alert message between frames T2.

Fig. 1 illustrates an exemplary architecture for broadcasting an alert service in an audiovisual digital program broadcasting system within a single-frequency plate according to the present invention.

The present invention is described in a broadcast system conforming to DVB-T2, acronym for Digital Video Broadcasting - Terrestrial Second Generation. The present invention is also applicable in audiovisual broadcasting systems that conform to other broadcast standards.

The system according to the example of FIG. 1 comprises at least one multiplexer 11 which multiplexes audiovisual services to be broadcast.

The multiplexer 11 encodes and multiplexes, for example, x services marked Servi and Serv2 to Servx, as well as a service denoted ServEWS that includes the audiovisual program to be broadcast in the event of an alert.

In a variant, the system comprises a second multiplexer 13 which multiplexes at least the audiovisual alert service to broadcast ServEWS instead of the multiplexer 11.

Multiplexer 11 forms, for example, three audiovisual data streams denoted TS1, TS2 and TS3. The audiovisual data stream streams TS1, TS2 and TS3 are streams of the TS (Transport Stream Acronym) type and conform to the ISO 13818 standard.

According to the variant, the multiplexer 13 encodes and multiplexes for example the services marked Servi 1, Servl2 and ServEWS.

The multiplexer 13 forms, for example, two audiovisual data streams denoted TS1 and TS12. The audiovisual data streams TS1 and TS12 are streams of type TS.

The data streams formed by the multiplexer 11 are processed by a T2 gateway 12 compliant with the DVB standard in its version 2 and which forms a stream called T2-MI stream. A T2-MI stream consists of a set of isolated physical layer tunnels. Each tunnel contains a multiplex of programs corresponding to a stream TS within the meaning of version 1 of the standard. The T2-MI stream is therefore composed of the different programs to be broadcast on a given region and the alert service. The T2-MI stream formed by the T2 gateway 12 is subsequently called the T2-T2 stream. Main MI. This T2-MI stream comprises the services broadcast when no alert service broadcast command is generated as well as the alert service which is not broadcast when a broadcast command of the alert service does not exist. is not generated.

According to the variant, the data streams formed by the multiplexer 13 are processed by a gateway T2 denoted 14 which also conforms to the DVB standard in its version 2 and which forms a stream T2-MI. The T2-MI stream formed by the T2 gateway 14 is subsequently called secondary T2-MI stream.

The T2-MI stream (s) formed by the T2 gateway 12 or the T2 gateway 14 are transferred in accordance with the present invention to an EWS alert service insertion module noted 10.

The transfer of the T2-MI flow (s) formed by the T2 gateway 12 or the T2 gateway 14 is performed via a satellite link. Satellite broadcasting is just one example, any other means of dissemination that can be used. The advantage of satellite is that it allows wide coverage of a set of potentially numerous transmitters that are far apart. Depending on the territory to be covered, it may be envisaged a diffusion by optical fiber for example.

A module for generating an alert service 17 generates dispatch commands for the alert flow to the alert service insertion module 10. The generation module of an alert service 17 is capable of to generate the service noted ServEWS to the multiplexer 11 or 13 or not if the alert service is generated by another device not shown in FIG. 1.

According to the present invention, the alert service insertion module EWS 10:

- obtains frames including the alert service and other services,

- associates a mark for each frame,

- identify identifiers of audio and video component packets of the alert service,

- identify identifiers of audio and video component packets of other services,

receives a command to broadcast an alert message,

- stores video and audio packets of the alert service from the first frame mark after receiving the broadcast command of an alert message,

- replaces, from the second frame mark following the reception of the broadcast command of an alert message, all the packets of the components video and audio services other than the alert service by the alert service packets stored in the backup memory and replace audio and video component packet identifiers of the alert service respectively by the packet identifiers of the audio or video component of the replaced packet to form a new frame.

The EWS alert service broadcast module 10 transfers the T2-MI stream thus formed to a processing and transmission equipment for broadcast 15.

It should be noted here that, for the sake of simplification, only one EWS alert service broadcasting module and one processing and transmission equipment for a broadcast are shown in FIG. 1. In reality, the system includes an EWS alert service broadcast module 10 and processing and transmission equipment for SFN plate broadcast.

Fig. 2 represents an insertion module of an alert service for a synchronous terrestrial broadcast within a single-frequency plate according to the present invention.

The insertion module of an alert service 10 comprises a communication bus 201 to which are connected a processor 200, a non-volatile memory 203, a random access memory 202, a communication or input interface 204 with the T2 gateways 12 and 14 and a communication or output interface 205 with the processing and transmission module 15.

The non-volatile memory 203 stores the software modules implementing the invention, as well as the data for implementing the algorithm that will be described later with reference to FIGS. 3.

More generally, the programs according to the present invention are stored in storage means. This storage means is readable by the microprocessor 200.

When the insertion module of an alert service 10 is powered up, the software modules according to the present invention are transferred into the random access memory 202 which then contains the executable code of the invention as well as the data necessary to the implementation of the invention.

Through the interface 205, the insertion module of an alert service 10 transfers the modified stream to the processing and transmission module 15 for broadcasting. All or part of the steps of the algorithm described below with reference to FIGS. 3 can be implemented by software by executing the steps by a programmable device such as a microprocessor, a DSP (Digital Signal Processor), or a microcontroller or implemented in a component such as a Field Programmable Gate Array (FPGA) or a ASIC (Application-Specific Integrated Circuit).

In other words, the insertion module of an alert service 10 includes circuitry which allows the insertion module of an alert service 10 to execute the steps of the algorithm of FIGS. 3.

Figs. 3 represent an example of an algorithm for synchronous terrestrial broadcasting within a single-frequency plate according to the present invention.

More specifically, the present algorithm is executed by the processor 200 of the insertion module of an alert service 10.

In step E300, the processor 200 detects the reception of the T2-MI streams of the T2 gateways 12 and 14 containing time markers for an SFN broadcast. The time markers are, for example, T2-MI-timestamp packets.

In step E301, the processor 200 aligns the T2-MI streams using the time information of the T2-MI-timestamp packets. For this, the processor 200 determines from information stored in the RAM 202, the unique identifier of the alert service and the T2-MI stream that includes the alert service. This information is for example and in a non-limiting manner stored during the installation of the insertion module of an alert service 10.

When the alert service is included in the main T2-MI stream, the processor 200 does not execute step E301, the main T2-MI stream already being aligned.

When the alerting service is included in the secondary T2-MI stream, the processor 200 executes step E301 and aligns the main T2-MI stream and the secondary T2-MI stream.

In the next step E302, the processor 200 unencapsulates the T2-MI flows to provide TS streams. A T2-MI stream includes T2-MI data packets such as T2-MI timestamp synchronization packets, signaling packets including the current named T2-MI L1 packet which provides information on the T2-MI flow structure and packets called Baseband Frames (BB), containing data from the MPEG-2 TS streams of the different tunnels. T2-MI packets are organized in T2 frames, each T2 frame contains a T2-MI timestamp packet, a current T2-MI L1 packet, and baseband packet frames.

It should be noted that, in a variant, the processor 200, instead of receiving T2-MI streams, directly receives TS streams with time markers corresponding to the standard used for broadcasting. These markers are, for example, Megaframe Information Packet (MIP) packets in the case of a first-generation DVB-T broadcast. In this case, the processor 200 does not execute the steps E300 to E302.

In the next step E303, the processor 200 associates a mark for each frame T2 of each decapsed TS stream.

An example is given with reference to FIG. 4.

Fig. 4 shows an example of a T2-MI stream received and processed according to the present invention.

In the example of FIG. 4, a T2 frame of a T2-MI stream comprising three tunnels denoted PLPO, PLP1 and PLP2 is shown.

The PLPO tunnel includes service data PI, P2 and P3 which have been multiplexed, the PLPL tunnel includes data Pl1, P12 and P13 of the service Serv2 which have been multiplexed and the PLP2 tunnel includes data P21, P22 and P23 Serv3 service that have been multiplexed.

A mark 40, present in each frame T2, is duplicated to the first packet

TS of each tunnel. The PLPO tunnel is marked by the mark 41, the PLPL tunnel is marked by the mark 42 and PLP2 tunnel is marked by the mark 43.

In the next step E304, the processor 200 searches the de-encapsulated T2-MI stream comprising the alert service, the unique identifier of the alert service and stores the PIDs (packet identifier in English and packet identifier in French). ) of the video component and audio components of the alert service. The identifier is called service id.

In the next step E305, the processor 200 searches in the de-encapsulated T2-MI stream, the unique identifiers of the other services and stores the PIDs of the video component and the audio components of the other services of the main stream.

When this is done, processor 200 proceeds to step E306 of FIG. 3b.

In step E306, the processor 200 checks whether a broadcast command for an alert message is received. The broadcast command of the alert message is for example included in one of the T2-MI streams received and is generated by the alert service generation module 17.

If no command to broadcast an alert message is received, no processing is performed on the different streams TS. They are encapsulated in packets keeping the same T2-MI structure as the T2-MI flows at the input of the insertion module of an alert service 10. Thus, the BBframes have the same size, the T2 packets -MI have the same counters.

If a broadcast command for an alert message is received, the processor 200 proceeds to step E307.

In step E307, the processor 200 stores the packets of the video component and audio components of the alert service from the frame mark T2 following the reception of the broadcast command of an alert message. Other alert service packets are not backed up.

Fig. 5 represents the reception of a command for broadcasting an alert message between frames T2.

In the example of FIG. 5, an alert message 50 is received after the frame mark T2 noted 51 and before the reception of the frame mark T2 52.

The processor 200 stores in step E307 the packets of the video component and audio components of the alert service from the T2 frame mark 52.

In the next step E308, the processor 200 counts, for each frame T2, the number of packets TS stored in step E307. This number is called Nb_package_alert.

In the next step E309 and from the following frame mark T2, in the example of FIG. 5, the frame mark denoted 53, the processor 200 identifies the packets of the different streams TS contained in the main stream T2-MI.

In the next step E310, the processor 200 replaces all the PID packets of the video and audio components of the other services than the null packet alert service.

In step E311, the processor 200 counts, for each frame T2 of the main stream T2-MI, the number of packets TS of each of the streams TS of the main stream T2-MI. For each TS stream of the main T2-MI stream, this number is called Nb_package (i) or i identifies a stream TSi of the main T2-MI stream. In the next step E312, the processor 100 calculates for each TSi, the ratio between the number of packets of the alert service and the stream TSi according to the following formula:

. Number of packages (i)

ratw (i) = Nb_pa-e-t-alert

It should be noted here that the result of this division not being an integer, the processor 200 defined then remains (i) the remainder of the Euclidean division ^Nb -P ^a ^ ^uet ^ _

Nb_paquet_alerte

In the next step E313, the processor 200 calculates, for each stream TSi, the duration of a packet TS in PCR time. Time tagging, in the form of packets containing a PCR field, is described in ISO 13818-1.

PCR stands for "Program Clock Reference".

For this, the processor 200 uses the PID containing the PCR of the first service of the stream TSi. At each new value PCR (n), where n is PCR field index, the processor 200 determines: Diff = PCR (n) - PCR (nl), counts the number of packets TS between two PCR values: NbPackPCR (i) and performs the Euclidean division of Diff by NbPaquetPCR (i). The quotient is called step pcr (i), the rest remains_pcr (i).

The processor 200 performs a Euclidean division of Diff by NbPaquetPCR. The quotient is called step_pcr (i) and the rest remains_pcr (i).

The processor 200 timestamps in PCR time all the packets of the stream TSi. The timestamp TimePcr of the package j realized is the following:

TimePcr (0) = 0 and residu_pcr = 0 for the first packet containing the T2 frame mark following receipt of the alert message namely the numbered frame 52

residu_pcr j + l) = residu_pcr j) + remainder_pcr (i),

if residu_pcr (j + l) <NbPackPCR then TimePcr j) = TimePcr j-l) + step_pcr (i)

Otherwise residu_pcr j + l) = residu_pcr (j + l) - NbPackagePCR

TimePcr j) = TimePcr j-l) + step_pcr (i) + l

When this is done, the processor 200 proceeds to step E319 of FIG. 3c.

In step E319, the processor 200 detects a frame mark T2.

In the next step E320, the processor 200 reads the first packet of the alert service stored during the previous frame T2 and stores it in a FIFO memory.

In the next step E322, the processor 200 defines the following variables Interval (i) = ratio (i), residual (i) and the packet counter cpt (i) = 1.

In the next step E323, the processor 200 increments the corresponding counter cpt (i) by one unit of each stream of each stream TSi. In the next step E324, the processor 200 checks whether the counter cpt (i) = Interval.

If so, processor 200 proceeds to step E325. If not, processor 200 returns to step E323.

In step E325, the processor 200 reads the next received packet.

In the next step E326, the processor 200 updates the variable residue (i): residue (i) = residue (i) + remainder (i).

In the next step E327, the processor 200 checks whether residu (i)> ratio (i). If not, processor 200 proceeds to step E329. If so, the processor 200 proceeds to step E328 and updates the residue variable (i): residu (i) = residual (i) - ratio (i).

In the next step E329, the processor 200 updates the interval variable (i): interval (i) = ratio (i) + l.

In step E330, the processor 200 reads the next packet of the alert service stored during the previous frame T2 and stores it in a FIFO memory.

Thus, all the alert service packets saved during the previous T2 frame are read and stored in the FIFO memory.

Once this is done, processor 200 proceeds to step E340 of FIG. 3c.

In step E340, the processor 200 checks whether the packet received from the stream TSi is a null packet and that the FIFO contains at least one packet of the alert service.

If not, the packet received from the TSi stream is not modified and the processor

200 goes to step E352.

If so, the processor 200 proceeds to step E341 and reads a packet in the FIFO.

In the next step E342, the processor 200 stores the packet read in step E341 in a so-called backup memory.

In the next step E343, the processor 200 checks whether the read packet TSi is a packet of an audio component. If the packet is a packet of an audio component, the processor 200 proceeds to step E344. The processor 200 replaces the null packet with the read alert service packet. If not, processor 200 proceeds to step E345.

In step E344, the processor 200 replaces the PID of the alert service packet stored in the backup memory with the first PID of the audio component of the stream TSi identified in step E305.

Once this is done, processor 200 proceeds to step E346. In step E345, the processor 200 replaces the PID of the alert service packet stored in the backup memory with the first PID of the video component of the stream TSi identified in step E305.

Once this is done, processor 200 proceeds to step E346.

In step E346, the processor 200 checks whether the next packet received from the stream TSi is a null packet. If the next packet of stream TSi is a null packet, processor 200 proceeds to step E347. If not, processor 200 proceeds to step E352.

In step E347, the processor 200 reads the next packet stored in the so-called backup memory. The processor 200 replaces the null packet with the read alert service packet.

In the next step E348, the processor 200 replaces the PID of the alert service packet stored in the backup memory with the next PID of the audio component of the stream TSi identified in step E305 if the read packet is an audio packet. or replace the PID of the alert service packet stored in the backup memory with the next PID of the video component of the stream TSi identified in step E305.

In step E349, the processor 200 checks whether all the components of each stream TS i have been processed. If not, processor 200 proceeds to step E350. If so, processor 200 proceeds to step E351.

In step E340, the processor 200 considers another component and returns to step E346.

In step E351, the processor 200 updates the packet continuity counters. For each PID of the services replaced, the first continuity counter is set to 0 and the flag discontinuity indicator is set to 1, then for each PID, the continuity counter is incremented by 1.

In step 350, the processor 200 updates the PCRs of the streams thus modified. The update of the PCR of the packet n is carried out as follows:

PCR (n) = PCR (n-1) + DeltaT (n, n-1) where DeltaT is the time between packet n and packet n-1.

For each service, the first updated PCR value is the original PCR of the inserted packet and the discontinuity flag is set to 1:

PcrOut (0) = PCRin (0) For n> 0 PCRout (n) = PCRout (nl) + DeltaT (n, n-1), DeltaT (n, nl) = TimePcr (n) - TimePcr (nl).

When this is done, the processor 200 proceeds to step E352 and re-encapsulates the packets in a T2-MI stream. The T2-MI stream has exactly the same structure as the original stream since processing is done at the TS level and there is no packet deletion or addition. The processing latency of the main stream is very low, so it is easy to use the characteristics of the incoming T2-MI stream.

When this is done, processor 200 returns to step E340.

The insertion of the alert service stops either because an alert stop message is received by the insertion module of an alert service 10 or because the alert service is not available. no longer present. In this case, the insertion module of an alert service 10 no longer performs any processing on the T2-MI stream.

Claims

1) Method for broadcasting an alert service in a system for broadcasting audiovisual digital programs within a single-frequency plate, characterized in that the method comprises the steps, performed by an insertion module of the service d 'alert:

- obtaining frames (E301, E301, E302) including the alert service and other services,

- association (E303) of a mark for each frame,

identification (E304) of the identifiers of the audio and video component packets of the alert service,

identification (E305) of the identifiers of the audio and video component packets of the other services,

receiving a command for broadcasting an alert message,

2) Method according to claim 1, characterized in that the replacement of all the packets of the video and audio components of the other services that the alert service by the alert service packets stored in the backup memory is broken down into steps of:

replacement of the null packets by the alert service packets stored in the backup memory. 3) Method according to claim 1 or 2, characterized in that the frames are T2 type frames and in that the method further comprises the step of encapsulation of packets of the new frame in a T2-MI stream. 4) Method according to claim 3, characterized in that the frames T2 comprising the alert service and the other services are included in at least one T2-MI stream and in that obtaining the T2 frames is performed by de-encapsulating the T2 frames of the T2-MI stream. 5) Method according to claim 4, characterized in that the T2 frames comprising the alert service and the other services are included in a single T2-MI stream.

6) Method according to claim 4, characterized in that the T2 frames comprising the alert service and the other services are included in two T2-MI streams, the frames of the alert service being encapsulated in a different T2-MI stream the T2-MI flow in which the T2 frames include the other services and in that the method comprises the step of alignment of the frames of the alert service and the frames of other services.

7) Method according to any one of claims 3 to 6, characterized in that the T2 frames are included in TS streams, the method further comprising the steps of:

determination of time tagging for each TS stream.

8) Method according to any one of claims 1 to 7, characterized in that the method further comprises the step of receiving a stop command of broadcast of an alert message and in that the packets other services are not replaced from the mark of the frame following the reception of the command to stop broadcasting an alert message. 9) Device for broadcasting an alert service in a system for broadcasting audiovisual digital programs within a single frequency plate, characterized in that the device comprises:

means for obtaining frames comprising the alert service and other services,

means for associating a mark for each frame,

means for receiving a command for broadcasting an alert message,

means for replacing, from the second frame mark following reception of the broadcast command of an alert message, all the video and audio component packets of the other services that the alert service by the alert service packets stored in the backup memory and replacing the audio and video component packet identifiers of the alert service respectively by the packet identifiers of the audio or video component of the replaced packet to form a new frame.