WO2021144247A1 - Opt-out method for a stream in a variable bit-rate multiplex, the stream consisting of a plurality of chunks, associated broadcast site and devices - Google Patents

Abstract

The invention relates to a method for opting out within a multiplex made up of a plurality of streams transmitting services, the method being implemented in a broadcast network at a broadcast site receiving a stream broadcasting a first service to be replaced by a second service from a first given point in time. The video component of the second service consists of a plurality of chunks with different bit rates. The method comprises at least the following steps implemented at at least one broadcast site: segmenting the first service into a plurality of time segments of at least the size of a chunk, and determining the bit rate of each segment of the first service, selecting, for each component of the service to be replaced and for each time segment, a chunk whose bit rate is at most equal to that of the first service of this segment, the selected chunk being split into packets that are inserted into the first stream, replacing each component of the first service with data packets from the selected chunk, reiterating the above steps until a second given point in time when the broadcast of the service of the first stream is resumed.

Description

DESCRIPTION

Title: Method of unhooking a stream in a variable rate multiplex, said stream consisting of a plurality of chunks, broadcast site and associated devices 1 - TECHNICAL FIELD

The field of the invention relates to the broadcasting of multimedia streams, and more particularly the switching from one stream to another stream. The invention applies in particular to the unhooking of a stream within a multiplex composed of multimedia programs / services at variable rate.

2 - TECHNOLOGICAL BACKGROUND

Nowadays, it is now possible to listen to an IP streaming radio (for "Internet Protocol") on terminals which also have a connection to an IP network, via a Wi-Fi interface or a 3G or 4G mobile network. for example. Such an audio stream transmission mode requires the use of a buffer or buffer memory in the receiving terminal, which generates a delay in the reception of the radio. New streaming modes such as HLS ("HTTP Live Streaming"), HSS ("Home Subscriber Service") and DASH ("Dynamic Adaptive Streaming over HTTP") are based on the use of small files of a few seconds of audio data, called “chunks” or songs, which creates a variable offset with the data broadcast live via RNT or FM, depending on when the user logs in.

It is also known practice to broadcast an audio stream produced from a succession of different streams which are synchronized with one another when switching from one to the other. It is currently possible to switch between two FM broadcasts, for “Frequency Modulation” in English, or between an FM broadcast (of the “Radio Data System” type RDS / FM synchronous) and an RNT digital terrestrial radio broadcast (DAB standards for “ Digital Audio Broadcasting ”or DMB for“ Digital Multimedia Broadcasting ”). Such a switchover is useful in radio for switching from a source transmitting a service of national scope to a source transmitting a service intended for local receivers. In all cases, the bit rate of the audio streams is the same, and the stream resulting from a switch has the same bit rate as the input streams.

It is known practice to broadcast multimedia programs by segmenting over time a source multimedia stream (for example of MPEG-2 TS type), into multimedia files. independent, small, called "chunks", then to format these chunks so as to broadcast them in the form of data in a multiplex conforming to the standards of the broadcasting network. The term multimedia content is understood to mean audio and / or audiovisual content which is reproducible by an audio and / or video terminal and which is broadcast in a service.

Thus, the fact that the data contained in the broadcast stream correspond to a plurality of independent files, each containing a “piece” of source stream, allows, in reception, an adaptability of high performance reading and restitution for the corresponding linear contents. Indeed, these independent files, or chunks, can be read autonomously, independently of each other.

In other words, a reproduction, on a terminal of a user, of a linear multimedia content, can start from any of these chunks (which starts with an image encoded in so-called “intra” mode, not requiring the knowledge of a previously coded image) thus offering mobility functionalities such as continuity of service, or “backtracking”. The segmentation of a content into a plurality of chunks is known more particularly under the name “Adaptive Bitrate Streaming”, in the “broadband” domain, that is to say for the transmission of client-server type data, in order to to provide (for example for downloading of the HTTP or FTP type), in response to a request from a user, a content adapted according to the capacities of the rendering terminal. The H LS, DASH and Smooth Streaming technologies are for example based on this so-called “Adaptive Bitrate Streaming” technique.

On the other hand, this segmentation technique is not currently used in the field of "broadcast", that is to say of the digital broadcasting of services in which the same source stream is intended for a plurality of users. , via a transmission site that can be picked up by receivers in its coverage area.

To replace or drop off in an MPEG TS type multiplex made up of programs / services at variable rate, known as “VBR”, acronym for “Variable Bit Rate”, within an SFN multiplex there are currently two solutions:

- either transcode all the programs, - or retranscribe the program to be replaced (or unhooked) at constant speed at the head of the national network in order to be able to replace it with another program downstream (on the transmission site, etc.)

It is known that the current drop-off or replacement systems in an SFN or MFN multiplex perform the exercise in a constant bit rate coded service, also called CBR mode (acronym for "Constant Bit Rate"), for a dropout remaining at the level. MPEG-TS. VBR type drop-off systems are also known, but these go through coding / decoding phases of all the programs.

It turns out that such processing on the programs to be broadcast is long and requires significant computing power. It is therefore desirable to seek another solution which does not use transcoding or substitution processing in CBR mode.

3 - OBJECTIVE

The invention proposes to replace (or unhook) an MPEG-TS service coded at variable bit rate by a spot at variable bit rate in the form of a file. This main idea consists in using the coding set up for the broadband (DASFI, FILS, ...) to divert it from its primary use in order to provide the best video quality according to the space available in a broadcast multiplex, and this deterministically to meet the need to drop off in an SFN broadcast network.

4 - SUMMARY

According to the invention, there is thus proposed an off-hook method within a multiplex composed of a plurality of streams transmitting services, said method being implemented in a broadcasting network at a broadcasting site receiving. a stream broadcasting a first service to be replaced by a second service from a first determined time. The video component of the second service consists of a plurality of chunks having different bit rates. The method comprises at least the following steps implemented at the level of at least one broadcasting site:

- segmentation of the first service into a plurality of time segments of at least the size of a chunk, and determination of the bit rate of each time segment of the first service,

- selection for each component of the service to be replaced and for each time segment of a chunk whose throughput is at most equal to that of the first service of this time segment, the selected chunk being split into packets which are inserted into the first stream,

- replacement of each component of the first service by data packets from the selected chunk,

reiteration of the above steps until a second determined moment called “hanging up” during which the broadcasting of the service of the first flow is resumed. Thus, the invention, according to its various embodiments, takes advantage of the advantages of the various techniques of broadcast broadcasting and access to multimedia content, in order to optimize the reproduction of a linear service on a user terminal, on the move. According to a first embodiment, the chunks of the video component of the second service are coded according to a plurality of different bit rates and constitute a series of streams each having a given bit rate, the selection step consisting in choosing the stream whose bit rate is at most equal to the bit rate of the first service of this time segment. In this way, it is possible to ensure maximum quality for the service to be inserted.

According to another embodiment, the step of determining the throughput of each time segment takes into account the data of the stuffing packets, so as to use them to insert therein data packets originating from the selected chunk. In this way, the method uses unused bytes in the stuffing packets to replace them with payload data making it possible to improve the quality of the service to be inserted. According to another embodiment, the unhooking method comprises a step of detecting the unhooking of at least two streams triggering a step of selecting a stream which benefits from the stuffing packets in order to insert therein data packets from the selected chunks. . In this way, the insertion step is facilitated by focusing only on a single flow.

According to an alternative embodiment, the off-hook method comprises a step of detecting the off-hook of at least two streams triggering a step of equitable distribution of the stuffing packets within said streams in order to insert therein data packets from the selected chunks.

According to another embodiment, the method comprises a step of counting the different packets of the components of the stream broadcasting the first service, the cumulative number of packets of each component being used to determine the throughput of each time segment of the first service. In this way, it is easy to calculate the available bit rate of the stream whose service is to be replaced.

According to another embodiment, the step of determining the bit rate of each time segment is carried out by storing the first service in a delay line, the depth of which is almost equal to the duration of a chunk. The use of a delay line greatly facilitates the substitutions of data packets, and the counting of these packets.

According to another embodiment, the off-hook method comprises a step of inserting empty packets into the stream after the last chunk packet, these empty packets having values of the “continuity number” field to ensure continuity between the value of the last chunk. packet and the value of the first packet sent by the first stream at the second determined time.

According to another aspect, the invention relates to a broadcasting server having means of receiving a multiplex composed of a plurality of streams transmitting services and having different bit rates and a means of broadcasting said multiplex over a determined region, a said streams transmitting a first service to be replaced by a second service from a first determined moment, the video component of this second service consisting of a plurality of chunks having different bit rates, characterized in that said server comprises the means following:

means for segmenting the first service into a plurality of time segments of at least the size of a chunk, and means for determining the throughput of each segment of the first service,

- selection means for each time segment of a chunk whose bit rate is at most equal to that of the first service of this time segment, the selected chunk being split into packets which are inserted into the first stream,

means for replacing the first service with data packets from the selected chunk, the broadcasting means broadcasting the data packets from the selected chunk instead of the first service on the stream considered.

In another embodiment of the invention, there is provided a computer program product, comprising program code instructions for implementing. implementation of the method described in the preceding paragraphs, by the receiving apparatus, when said program is executed on a computer.

5 - LIST OF FIGURES

Other characteristics and advantages of the invention will become apparent on reading the following description, given by way of indicative and non-limiting example, and the appended drawings, in which:

[Fig 1] - Figure 1 shows a system for broadcasting a multiplex of streams having different bit rates according to an exemplary embodiment;

[Fig 2] - Figure 2 illustrates the main components of a remote server, according to an exemplary embodiment;

[Fig 3] - Figure 3 shows an example of a flowchart of the main steps of an off-hook method to a local service;

[Fig 4] FIG. 4 illustrates the analysis of a stream in the delay line with a view to replacing the multimedia content of this stream during a given duration;

[FIG. 5] FIG. 5 represents a diagram describing the selection of the chunks and the replacement of the service of the national flow by packets resulting from the coding of the selected chunks;

[Fig 6] - Figure 6 represents the different audio and video streams of a regional service for a determined duration.

6 - DETAILED DESCRIPTION OF THE INVENTION

In all the figures of this document, identical elements and steps are designated by the same reference. The general principle of the technique described is based on the new and clever use of the segmentation of video content into chunks and then on the splitting of each chunk into a plurality of data packets, the payload of which is inserted in the packets of data. a stream forming part of a plurality of streams of a multiplexed broadcast network.

With reference to FIG. 1, there is shown a system for broadcasting a stream multiplex transmitting services having different bit rates. A flow is considered as an uninterrupted series of data packets having a link between them to identify them, the same reference for example. A stream can transmit an audio and / or visual program or a service comprising several components. This multiplex is for example, of the MPEG TS type in an SFN network, acronym for “Single Frequency Network”. The various so-called “national” streams of the multiplex are sent by a network head 10, drawing 11 represents an example of a stream transmitting data over time, the quantity of information transmitted in each stream varying over time. The network head transmits the multiplex to a broadcasting network, optionally via a satellite 12. Said broadcasting network is advantageously made up of broadcasting sites 13 which are distributed geographically over an entire territory, each broadcasting site covering a given region. A broadcasting site can directly transmit by radio on a given region, or supply radio transmitters, it is then also called a “plate head”. The radio signals transmitted by the broadcasting sites are locally received by terminals and the services transmitted in the various streams can then be reproduced on a screen and an audio system. Certain broadcasting sites 13 receive one or more so-called “regional” streams, the multimedia content of which must be broadcast locally, ie accessible only by the terminals located in the region covered by this site. The regional streams are produced by a regional service server 14 and are transmitted either by in a specific stream sent by the national network head 10, or in a local stream 15 which can be based on a wired link, ETHERNET for example. The service to be inserted can be transmitted when it is intended to be reproduced by terminals or, be downloaded into a data memory of the broadcasting site and read from this memory during off-hook.

According to the invention, the coding of the components of a service in multi-bit rate mode used for the OTT domain (DASH, HLS, etc.) is used to replace or unhook a program encoded at variable bit rate in a multiplex. broadcast. According to a first embodiment, the broadcast multiplex is transported to transmission sites which are equipped with processing units capable of replacing a VBR service by a service coded in multi-rate components. The video component can be encoded at these sites at different CBR rates. This coding operation can be carried out centrally in order to carry out the coding only once. It is then all of the video components encoded in the different available bit rates which are then routed to the dropout sites. A first application of the present invention is to allow an advertising dropout at the broadcasting sites 13, in this way the advertising slots can be personalized according to the region where the streams are broadcast.

Fig. 2 illustrates the main components of a remote server 20 equipping a broadcasting site 13. According to this exemplary embodiment, the server 20 comprises a central unit ALU 21 connected to an executable program memory PM 22, an HD hard disk 23 containing a database for non-volatile data storage. The server 20 also contains an I / O interface 24 for communication with the receiver 1 via a computer network. The server 20 is connected to a radio transmission and reception means 25 making it possible to receive at least one national stream, transmitted for example by a satellite, and to transmit regional streams in a given region. Such a server makes it possible to switch from a national flow to a regional flow and vice versa. It is not excluded that the means of transmission differ according to the broadcasting site, the regional and / or national flows being able to be received and / or transmitted by radio or by wire connection. In order to analyze all the streams of the multiplex sent by the network head 10, the remote server 20 has a delay line making it possible, for a given duration, to determine the origin of the data packets broadcast. The invention makes it possible in particular not to go off hook to a flow at CBR bit rate, and to insert within a VBR stream whose bit rate is variable a content whose bit rate is also variable, and that in a deterministic manner. In this way, the integrity of the SFN network is safeguarded.

After having presented the different hardware devices, we will now explain how they cooperate.

Fig. 3 shows an example of a flowchart of the main steps of a method of going off hook to a local service, according to the invention. These steps are advantageously carried out by software modules which are executed at the level of the remote server 20. Firstly and in step 3.1, this server receives an off-hook signal which can be transmitted by the national network head 10, or by a local signal coming from a regional service server 14, or even a clock signal indicating an off-hook at a given moment. The off-hook signal comprises at least the identifier of the flow whose service is to be replaced and the identifier of the service to be replaced. insert (or signaling means making it possible to find the service precisely, at the level of an Internet site for example). Each component of the service to be inserted into the identified stream consists of chunks of a duration almost equal to the duration of the delay line. The method which is the subject of the present invention knows the duration of a chunk by analyzing the content of the chunk or by interrogating a configuration server, and deduces therefrom the duration of the delay line. This duration is also called: “depth of the delay line” and is expressed in seconds or its submultiples. The segmentation of content into chunks is a technique known per se in the field of Broadband, the recommended standard is described by the DVB-DASH standard, which is given only by way of example.

All the data packets of the delay line are continuously analyzed (step 3.2) in order to determine which flow corresponds to a particular packet. It is then possible to calculate the quantity of multimedia data packets belonging to the stream which is identified in the off-hook signal, in other words: its bit rate measured in Mbps. Fig. 4 illustrates the analysis of a stream in the delay line with a view to replacing the multimedia content of this stream during a given duration, typically one second. Each component of the service to be replaced is divided into segments noted: "Seg.l",

"Seg.2", ... "Seg. n-1 ”,“ Seg. n, the duration of regional service which corresponds to the duration of the dropout noted: “Duration_D. ". It is recommended that the formats of the video components of the service to be replaced and of the service to be inserted be compatible or even identical to avoid the appearance of display artifacts during pick-up and hang-up. The delay line makes it possible to count the number of packets of the national flow whose service is to be replaced, and to determine the flow rate of the flow during the given duration. The packets transport in particular the following elements: the video component, the audio components, the subtitle components, the stuffing packets (PID 8191) of the multiplex. The quantity of packets is represented by a gray area which varies in height with time, thus showing the fluctuations in the data rate as a function of time. In the example represented by FIG. 4, each segment has a certain rate:

- segment number 1 has a speed of 1 Mbps,

- segment number 2 has a speed of 4 Mbps, - segment number 3 has a speed of 2 Mbps, ...

- segment number n-1 has a speed of 3.3 Mbps,

- segment number n has a speed of 2.5 Mbps.

Once the rate of the segment which is stored in the delay line has been determined, the method which is the subject of the present invention selects the chunks representing the regional service to be inserted so as to make maximum use of the bandwidth available at the level of the national stream (step 3.3 ), in other words the selected chunks are those whose bit rate is at most equal to that of the content present in the delay line and which comes from the national stream broadcast by the network head 10. Once the selection has been made, the payload of the packets of each component of the national service stored in the delay line is replaced by the packets coming from the encoding of the selected chunk (step 3.4). In this way, the national service is replaced by the regional service according to the principle of deterministic remultiplexing. For each segment, the method which is the subject of the invention selects the chunks of each component of the regional service which best correspond to the bit rate available in the national flow.

Fig. 5 presents a diagram describing the selection and the replacement of the multimedia content of the national stream by a content composed of chunks and coming from a regional service server. The upper part is composed of four lines with different thicknesses to represent the fact that the chunks of the same regional service are coded in a plurality of different rates, for example: 1, 2, 3 and 4 Mbps. As can be seen in the figure, the packets of segment 1 whose rate has been measured at 1 Mbps are replaced by the data packets produced by encoding a chunk having a rate of 1 Mbps. Likewise, the packets of segment 2, the bit rate of which has been measured at 4 Mbps, are replaced by the data packets produced by the coding of a chunk having a bit rate of 4 Mbps. Finally, the packets of the last segment whose bit rate has been measured at 2.5 Mbps are replaced by the data packets produced by the encoding of a chunk having a bit rate of 2 Mbps, the packets of a chunk having a bit rate of 3 Mbps not having enough room to be inserted into the national stream. For segments n-1 and n, there is effectively room left in the segment since the bandwidth has not been completely consumed, packets of jam (PID8191 are then produced. The arrows represented in the figure illustrate the origin of the chunks whose packets replace the packets of the national flow.

Steps 3.2, 3.3 and 3.4 are repeated until the moment when a second so-called hang-up signal is reached (step 3.5). This reiteration is illustrated by the dotted arrows which loop back to step 3.2. Let's take an example, if the service to be replaced lasts 20 seconds and the duration of each chunck is 1 second, steps 3.2, 3.3 and 3.4 will be repeated 20 times. For each loop, the available bit rate is recalculated making it possible to offer a variable bit rate: first chunk: 1 mbps, second chunk: 4 mbps, third chunk: 2 Mbps. This reiteration is carried out until the moment of hanging up. The on-hook signal can be sent by the national network head 10, or by a local signal coming from the regional service server 14, or even a clock signal indicating the end of the broadcasting of a local service. On receipt of this signal, the site 13 stops transmitting the regional service and broadcasts the national service (step 3.6).

According to a refinement, the method counts the stuffing packets (detectable by their PID having the value “8191”) present in the delay line and takes these packets into account to determine the available bit rate of the stream whose service is to be unhooked. This improvement is carried out at a certain point in the flowchart shown in FIG. 3, and appears as step 3.2bis.

The method determines the number of stuffing packets present in the delay line, in this way, a tolerance is preserved to insert all the packets of the chunks if the space were to run out. Let us take the example of the last segment which has a rate of 2.5 Mbps, it is possible that there are enough padding packets in the SFN multiplex to reach the rate of 3 Mbps and thus use a chunk with a rate of 3 Mbps. In this way, we can make optimal use of the space available within the multiplex so as to select a chunk whose coding has a better quality.

As a function of the number (called “PAR”) of packets of the component of the service to be replaced, the method selects a chunk having a number of packets (called “PC”) closest to this number.

- If the number "PC" is less than or equal to "PAR", insertion is possible without even using padding packets. - If the number “PC” is slightly greater than “PAR”, then the method calculates whether the number of padding packets is sufficient for their payload to be sufficient to contain the surplus in packet data.

Adding packets to the stream makes it possible to increase the bit rate of this stream and to broadcast better quality services. Taking into account the stuffing packets within the delay line is only possible if only one flow is off hook at a time. In the case of multiple stalls, the use of the stuffing packets is reserved for one of the services or distributed in a known manner between the services which go off hook.

Fig. 6 represents the different audio and video streams of a regional service for a determined duration, one or more minutes. This service can be an advertising page, or a meteorological bulletin, or an alarm message (fire, kidnapping, storm, etc.), or any other advertisement having a local character. As can be seen in Fig. 6, this regional service is coded and presented to the replacement system by a plurality of different coding rates, like what DVB-DASH offers for example, but any other neighboring method can do the trick; DVB-DASH offers an encoding of a service whose components are encoded at different bit rates by section of finite periods commonly called "Chunk", all returned in the form of a file. This regional service can be extended by a few images (for example by the duration of a chunk) to compensate for a divergence in duration between the spot to be replaced which would be a few images longer than the replacement spot. This addition can consist of “neutral” images or identical to the dividers contained in the program affected by the replacement.

MPEG-TS packets from chunks include the following components:

- the video component,

- audio components,

- the subtitle components (not shown in the figure).

All of these service components need to be replaced. The counting of the packets and the determination of the rate of each stream (step 3.2 of FIG. 3) is carried out by analyzing the PIDs of the packets recorded in the delay line. This counting is carried out periodically, the period being substantially the duration of a chunk. The process object of the invention counts the different packets of all the components of a flow intended to pick up, namely:

- the number of video packets of the service to be picked up,

- the number of packets for each audio component,

- the number of packages for all the other components of the service, and

- the number of padding packets (PID 8191).

The determination of the throughput of each segment of the service to be replaced is calculated by cumulating the numbers of packets of each component of the stream broadcasting the first service, and by dividing this cumulative value by time.

The replacement of the packets can be carried out by writing the new values in the memory of the delay line or at the output thereof. The replacement of the payload of the packets is accompanied by the modification of the signage. Indeed, during each packet replacement, the module object of the invention modifies the value of the PID of the packet to adapt it to its new payload. The PCR and PTS stamps are recalculated by aligning themselves with those of the components of the component of the flow to be replaced. The module copies the value of the “continuity_counter” of the first packet to be replaced in the replacement one and increments this value in the following packets.

As the broadcast network, of the SFN type for example, consists of variable bit rate streams, it is necessary to provide it with a specific marker in a packet called MIP, this marker is used to synchronize the entire network of the SFN plate, using a common time reference. By synchronizing by very precise clock systems (GPS or other), it is possible to recalculate the value of the PCRs during simple stalls.

This common temporal reference allows deterministically to:

- size the delay line according to the duration of the chunks of the replacement spots,

- to recalculate the PCR stamps when unhooking.

This common time reference comes from the SFN multiplex itself, in this case its bit rate, by taking the information from the MIP packets. The flow of multiplex is calculated, using the data related to the modulation found in the “tps_mip” field.

FLOW = (9/2176) x ([Band x Modulation x FEC x Packet size] / (1+ guard interval]), where:

- Band: channel bandwidth which can be 5, 6, 7 or 8 MHz,

- Modulation: number of bits per carrier,

- FEC: report giving the number of useful bits for the number of bits transmitted,

- Packet size: 188 or 204 bytes.

The calculated bit rate values typically vary between 4 Mbps and 32 Mbps. Annex 1 presents a summary table of the bit rates as a function of the modulation. The values in this table are given for MPEG-TS packets of 188 bytes. This appendix shows 960 millisecond chunks making up the replacement spot. This value is calculated for 40 millisecond frames, which produces 960 and 1000 millisecond chunks. This value may vary depending on the choice of the manufacturer of broadcasting installations and depending on certain countries where the number of frames per second may vary.

The size of the delay line is determined by the size of the chunks of the service to be inserted. Appendix 2 shows examples for one-second serve chunks. Preferably, the coding of a chunk consists of a GOP (acronym for "Groupe Of Picture", or group of images in French) made up of a single I image, followed by type P and B images. To overcome any problems with hanging up, an additional chunk is added at the end of the spot, which can be made up of neutral images. In addition, the last 2 video chunks are preferably devoid of B images, only made up of I and P images. This arrangement can be configured by the manufacturers.

The off-hook and on-hook orders are in-band commands via SCTE35 packets. The commands indicate from which image the system should pick up or hang up; the identifier used is the PTS stamp of the image. The module analyzes all received SCTE35 packets and, if the order is given to pick up or hang up, searches for the packet carrying the PTS field which exactly determines the instant of off hook or on hook. The first image of the instant of hanging up is detected at the input of the delay line, in this way, the module easily determines the last analysis period in the delay line, before reestablishing the national flow. In order not to create a time shift, the module checks and respects that the number of replaced images is identical to the number of replacement images. For this, the module, knowing the number of images to be replaced following the orders received, the PTS stamps increment all the “SDI” image periods (generally 40 ms at present), and the PTS stamp of hook-up and the PTS hang-up stamp, deduces the number of images to be replaced. The module hangs up to the nearest number of images to be replaced, even if the number of images of the replacement spot is not in line with the spot to be replaced. For this reason, the last two regional service chunks are encoded only I and P frames.

Let us take an example, if the spot to be replaced consists of 10 images and that the replacement one consists of 15 images, the module stops the replacement after 10 images without incident because the series of P images follow each other, they are not out of order, as are GOPs containing B images. Similarly, if it is necessary to use stuffing packets to absorb a surplus of packets to be introduced, the procedure is the same. Note that the duration of the sequences to be replaced is preferably expressed in multiple of one second. It is preferable that the on-hook image is not at the beginning of the delayed line, but this situation rarely occurs (actually once on "n", or n = (duration of the delay line) / (duration d When this situation occurs, there is a risk of seeing a visual artifact or a black screen for a short time. This makes it easier to update the signage and manage the values of the “continuity counter”. , an advertising sequence of 20 seconds, the hang-up will be processed at 200ms from the delay line; for a 30s spot, this will be processed at 30ms from the delay line ... Note that chunks can also last a value different from 960 ms while remaining a multiple of 40 milliseconds, it is a choice of the manufacturer who implements the solution.

To avoid the appearance of visual artifacts, one solution consists in extending the delay line by a small amount of data in order to create a memory (or "buffer" in English) anticipation, for example 200 milliseconds. In doing so, the national signal is delayed by a little more than the duration of the delay line, for example 1.2 seconds. It is thus possible to smooth the “continuity number” of the packets which are in this memory.

Once the last packet of the replacement image has been inserted, the module analyzes the “countinuity_counter” of this packet, analyzes that of the hang-up packet and inserts between these 2 packets as many empty packets as necessary to respect the continuity of this counter. Remember that this counter is modulo 16, so it will only be necessary to add at most 15 empty packets. This operation is performed for each component of the service to be replaced (video, audio, subtitles, etc.).

In the context of DTT, FMN type broadcasting transmitters are used, which rely on several specific channels. In this context, MFN transmitters transmit asynchronously, with no synchronization link between them, which excludes any deterministic process constraint in the replacement / processing system. For the MFN drop-off algorithm, it uses the same advertising drop-off process at the feet of an SFN transmitter. The nuance is located at the level of the temporal reference which is no longer resulting from the calculation from data of the MIP packet but from the PCR stamps of the service.

The flow calculation of the MFN multiplex is carried out from the parameters given by the PCR of the service to be picked up, and is indicated by the equation below, which is taken from the widely used ISO / IEC 13818-1 standard. in the field of broadcasting.

In this equation, the PCR value to be corrected is the PCR variable (i '). the data of this equation are:

- transport_rate (i): calculation resulting from the analysis of the MIP packet,

- i 'and i ": index giving the difference in bytes between the MPEG-TS packets containing the PCR stamps of the service,

- PCR (i "): value of the last PCR stamp encountered.

- system_clock_frequency: constant fixed at 27.106. This present embodiment is based on evaluating the available bit rate and replacing a chunk of a certain bit rate with a chunk having a bit rate of a higher value. The same reasoning can be held by reasoning in terms of the volume of data available. The method that is the subject of the invention calculates the available volume by counting the number of packets whose service is replaceable and replaces the stuffing data with payload data.

Although described through a number of detailed exemplary embodiments, the proposed devices include different variants, modifications and improvements which will be evident to those skilled in the art, it being understood that these different variants, modifications and improvements are part of the scope of the invention, as defined by the claims which follow. In addition, different aspects and features described above may be implemented together, or separately, or substituted for each other, and all of the different combinations and sub-combinations of aspects and features are within the scope of the 'invention. In addition, it is possible that certain devices described above do not incorporate all of the modules and functions provided for the embodiments described.

Finally, the present technique can be implemented in terrestrial MFN or SFN networks but also in DTH (acronym for “Direct to Home”) satellite networks or even cable networks.

Annex 1

Annex 2

Claims

1. An off-hook method within a multiplex composed of a plurality of streams transmitting services, said method being implemented in a broadcasting network at a broadcasting site (13) receiving a first service to be replaced. by a second service from a first determined moment, the video component of the second service consisting of a plurality of chunks having different bit rates, characterized in that it comprises at least the following steps implemented at the level of '' at least one distribution site: - segmentation of the first service into a plurality of time segments of at least the size of a chunk, and determination of the bit rate of each segment of the first service, - selection for each component of the service to be replaced and for each time segment of a chunk whose bit rate is at most equal to that of the first service of this time segment, the selected chunk being split into packets which are inserted into the first stream, - replacement of each component of the first service by data packets from the selected chunk, reiteration of the above steps until a second determined moment called “hanging up” during which the broadcasting of the service of the first flow is resumed. 2. Unhooking method according to claim 1; characterized in that the chunks of the video component of the second service are coded according to a plurality of different bit rates and constitute a series of streams each having a given bit rate, the selection step consisting in choosing the stream whose bit rate is at most equal at the rate of the first service of this time segment. 3. Unhooking method according to claim 1 or 2; characterized in that the step of determining the throughput of each time segment takes into account the data of the stuffing packets, so as to use them to insert therein data packets originating from the selected chunk. 4. An off-hook method according to claim 3, characterized in that it comprises a step of detecting the off-hook of at least two streams triggering a step of selecting a stream which benefits from the stuffing packets in order to insert therein packets of. data from selected chunks. 5. An off-hook method according to claim 3, characterized in that it comprises a step of detecting the off-hook of at least two streams triggering a step of equitable distribution of the stuffing packets within said streams in order to insert data packets therein. from selected chunks. 6. An off-hook method according to any one of the preceding claims, characterized in that it further comprises a step of counting the different packets of the components of the stream broadcasting the first service, the cumulative number of packets of each component being used for. determining the rate of each time segment of the first service. 7. An off-hook method according to any one of the preceding claims, characterized in that the step of determining the bit rate of each time segment is carried out by storing the first service in a delay line, the depth of which is almost equal to the duration of a chunk. 8. An off-hook method according to any one of the preceding claims, characterized in that it comprises a step of inserting empty packets into the stream after the last packet of a chunk, these empty packets having values of the "field". continuity number ”to ensure continuity between the value of the last packet and the value of the first packet sent by the first stream at the second determined moment. 9. Broadcast server (20, 13) having reception means (24; 25) of a multiplex composed of a plurality of streams transmitting services and having different bit rates and a means of broadcasting (25) of said multiplex on a determined region, one of said streams transmitting a first service to be replaced by a second service from a first determined moment, the video component of this second service consisting of a plurality of chunks having different bit rates, characterized in that said server comprises the following means: - means (21, 22) for segmenting the first service into a plurality of time segments of at least the size of a chunk, and means for determining the throughput of each segment of the first service, - means (21, 22) for selecting for each component of the service to be replaced and for each time segment of a chunk whose bit rate is at most equal to that of the first service of this time segment, the selected chunk being split into packets which are inserted in the first stream, - Means (21, 22) of replacing each component of the first service by data packets from the selected chunk, the broadcasting means broadcasting the data packets from the selected chunk instead of the first service on the stream considered. 10. Computer program product, comprising program code instructions for implementing the method described according to at least one of claims 1 to 8, when said program is executed on a computer.