WO2014131751A1

WO2014131751A1 - Method of splicing the scrambled streams

Info

Publication number: WO2014131751A1
Application number: PCT/EP2014/053613
Authority: WO
Inventors: Samuel Vermeulen; Frédéric MOUNIER
Original assignee: France Brevets
Priority date: 2013-02-27
Filing date: 2014-02-25
Publication date: 2014-09-04
Also published as: FR3002717A1; FR3002717B1

Abstract

The invention relates to a method and a system for splicing at a first instance T_S1 in a broadcasting system at least one first scrambled stream F_1e by means of a first control word CW₁ and at least one second scrambled stream F_2e by a control word CW₂ characterized in that it uses a same fixed value CW of control word to scramble simultaneously and over the duration of the splicing, at least partially the first stream F₁ and at least partially the second stream F₂, the control word CW being fixed for the duration of the splicing of the first stream to the second stream and in that in a given span after the instant of splicing T_S1, the messages ECM₂ associated with the second stream F₂ are broadcast.

Description

TITLE

REMOVAL PROCESS FOR FLOW STREAMS

The object of the invention relates to a method and a system for performing local stall better known as "splicing" on scrambling streams or "scrambling stream" without having to perform a decoding or descrambling of the stream in normal operation.

Program delivery systems allow service providers to insert advertising programs or short programs into nationally distributed programs before being transmitted to users.

In known practice, the systems and methods for performing the "splicing" process use a first device to descramble the first national stream, a second piece of equipment to perform "splicing" and a third piece of equipment to scramble the second stream of output after splicing. and disseminate programs locally.

The use of several devices leads in particular to increase installation costs, maintenance, latency in the dissemination of programs.

In the remainder of the description, the following acronyms are used:

CW: control word or "control word",

ECM: control message that contains criteria for access to a service and a control key or word, or "entitlement control message",

ECMG: a control message handler,

EMM: message that contains service access information, or "entitlement management message",

CP: designates a crypto-period,

SI / PSI: Information Service / Program Specific Information or "Service Information / Program Specifies Information".

The idea of the present invention is based in particular on the implementation of a method of stalling or "splicing" on scrambled flows that does not require having to descramble / rewrite the flows involved in the operation. The invention relates to a method for effecting the stall or "splicing" at a first instant T _S i in a system diffusing at least a first scrambled stream F _e by means of a first control word CW and at least a second scrambled stream F _2e by a control word CW ₂ characterized in that it uses the same value CW fixed control word to scramble simultaneously and during the duration of the splicing, at least partially the first stream Fi and at least partially the second stream F ₂ , the control word CW being fixed during the stall time T _s of the first stream to the second stream and in that, within a given time after the stall time T _S i, the ECM messages ₂ associated with the second stream F ₂ .

The value of the control word CW is, for example, determined by means of an algorithm common to the scrambling device of the first stream F and the scrambling device of the second stream F ₂ .

According to another embodiment, the CW value of the control word is determined from a table storing for a given moment, a control word value, the control word generator using said table M to partially scramble the first one. F flux and partially scramble the second flux F ₂ , for splicing.

The method can be used for stalling a first stream F to a second stream F ₂ and the method is characterized in that it comprises at least the following steps:

• at least partially scramble the packets of the first stream F to be broadcast, using a first control word CW- ,,

Determining a first stall point at the time of stalling T _s and triggering T seconds before this point, a scrambling mode using a fixed control word CW, in order to partially scramble the first stream F _;

Transmit the stall point information at the time of stalling T _s to the second stream F ₂ ,

• T ₂ seconds before the stall point at the time of stalling T _s , at least partially scrambling the flow F ₂ with the fixed control word CW calculated,

After the stall point at the time of stalling T _s , stop the broadcast of the ECM control messages associated with the first stream F and broadcast the ECM messages ₂ associated with the second stream F ₂ using the same PID packet indicator as the flag used for the ECMi messages of the first

The stall point T _s is, for example, determined from tables SCTE35 broadcast with the first stream F to the device generating the second stream F ₂ .

The first stream F is, for example, a national stream, the second stream F ₂ is a stream comprising a local program or an advertising program.

The process will choose for ΤΥι, integer values of crypto-periods. According to one embodiment, the first stream and the second stream being audio / video streams, stalling is performed on the packets containing the beginnings of images and audio frames.

The invention also relates to a system for performing the stall or "splicing" at a first instant T _S i in a system diffusing at least a first scrambled stream F _e by means of a first control word CW and a first scrambler and to less a second scrambled stream F _2e by a second control word CW ₂ and a second scrambler, the system is characterized in that it comprises at least the following elements:

A management means adapted to switch a CW control word random calculation mode to a CW control word fixed calculation mode and conversely, on receiving a parameter,

Means adapted to generate a fixed control word CW during a splicing time Ts, simultaneously for the first stream F and for the second stream F ₂ ,

A controller adapted to manage the ECM messages associated with the first stream F and the ECM messages ₂ associated with the second stream F ₂ .

The system according to the invention may comprise an algorithm adapted to generating one or more same fixed control word (s) CW to scramble the first stream F and to scramble the second stream F ₂ for a duration corresponding to the duration of splice.

The system can be equipped with a table M storing pairs formed by the value of a control word CW and a splice instant Ts. Other features and advantages of the device according to the invention will appear better on reading the following description of an example of embodiment given by way of illustration and in no way limiting attached figures representing:

FIG. 1 an exemplary architecture of the system according to the invention,

"Figure 2, a schematic diagram for two streams, the steps applied by the process during splicing.

The following description is given in the case of a scrambled national stream in which a provider wishes to insert local advertising programs. It is clear that the invention can also be used in any system comprising a first scrambled stream in which it is desired to insert advertising programs or short programs without having to descramble the streams.

On the national system side, the device 1 comprises a source of video signals 2 that will be transmitted to scrambling equipment 3. The latter operates, for example, on the basis of a signal called "scrambling sequence" which determines how the scrambling is performed, with a first CW-i control word. The scrambled signals, the first national stream, are broadcast via a network 4 to a local equipment 10. The national scrambler 3 is linked to one of the IF / PSI tables 5, a CW control word generator 6, a generator 7 messages

The scrambling sequence of the national stream F is generated and provided by a scrambling sequence generator which comprises in particular a pseudo-random generator initialized by a first control word CW-i, according to a method known to those skilled in the art. which will not be explained in the present description.

The local equipment 10 is equipped with a scrambling device 1 1 adapted to perform the scrambling of the local stream F ₂ by a scrambling sequence, using a second control word CW ₂ . The scrambling device 1 1 is connected with SI / PSI tables 12, a control word generator 13 CW ₂ , an ECM message generator 14 of F ₂ . The scrambled stream F _2e is transmitted to a "drop-out" or "splicer" 15 which also receives the scrambled stream F _e . At the output of the splicer, for example, at the beginning of the stall or "splice", the stream Fi _e and the messages ECMi of Fi _e , then the stream F _2e with the messages ECM ₂ , then at the end of the splice the stream Fi _e and associated messages ECM-i. The scrambling sequence of the local stream F ₂ is generated and provided by a scrambling sequence generator which comprises in particular a pseudo-random generator initialized by a second control word CW ₂ .

The two random control words CW and CW ₂ are not synchronized. They are generated, for example, every n seconds to vary the key or control word and they are transmitted to the decoder allowing access to the national program outside the local stall and local program during this stall before it the latter needs it so that a user can watch the program.

The idea implemented by the method according to the invention is based in particular on the use of a control word CW which will be fixed for a given duration corresponding to the duration Ts of splicing and which will be identical to scramble the first national F stream and to scramble the second local F ₂ stream. Thus, before executing the splicing step the two streams are scrambled with the same CW key or control word.

The scrambler at the national level and the scrambler at the local level are equipped with the same algorithm for generating fixed control words during the duration of the splicing.

Similarly to the national equipment, according to a first embodiment, the scrambler will be equipped with a fixed control word generation algorithm for the duration of splicing. According to another embodiment, the scrambling device will comprise tables memorizing for a given instant of splice Ts, a fixed control word to be used, the control word generator fetching this information, when it receives a parameter given the warning of a moment of stall.

For the implementation of the method according to the invention, the system requires, for example, as a prerequisite, the scrambling of certain audio / video packets only (a majority of them all the same) at the scrambling level. in order to preserve the image / audio frame headers necessary for local splicing according to techniques known to those skilled in the art.

The audio / video packets not to be confused are, for example, transport packets containing:

- A PES or Packetized Elementary Stream header (with or without PTS packet transport stream / DTS flags ....) - Standard MPEG-2 video headers:

o Sequence header and extension "header and extension"

o The header of the group of images or "GOP header"

o The header of the image and its extension "Picture header and extension"

o User data or "User data" (for the splicing of the display at the bottom of the screen or in English »closed caption»)

- Standard H.264 video headers:

o SPS (parameter set sequence)

o PPS (picture parameter set)

o AUD

o SEI supplemental enhanced information (for closed caption splicing)

o Slice header or Slice header

Audio standard headers (MPEG-1 Layer 2, AAC, DD / DD +) of the order of 7 bytes.

One way to carry out the steps of the method according to the invention is to equip the scrambling device of the first national stream and the local splicing / scrambling device of a common algorithm between these two devices, the algorithm being adapted to generate 2 same control word, a peer and an odd one.

The value of these 2 control words CWs is fixed during the duration Ts of the splicing and varies for each splicing. The calculation algorithm takes as input a parameter chosen so as to ensure the synchronization of the calculations of the control words made by the two devices. Thus, the parameter used to trigger the calculation of the control word may be the data related to the timestamp of the splice that is contained in the SCTE35 tables and thus accessible to both devices. In this case, the synchronization of the passage from the computation of the CWs of the random mode to the "computable CW" mode is carried out via the diffusion of the SCTE35 tables.

The method will then perform, for example, the following steps:

• At the level of the national scrambler, the process will proceed as follows:

the distribution of the SCTE35 tables, then the shuffling of the scrambling of the national stream Fi, from the "random CW" mode to the "calculable CW" mode.

For example, the switching between modes can be done X CP cryptoperiods preceding the splicing point corresponding to T _s , to ensure that the current ECM at the time of the splice conveys the predefined value CW for the CWsp peer control word and the predefined value for the odd CWsi control word, and thus makes it possible to hide the use of a fixed CW during several crypto-periods CPs corresponding to the duration of the splice.

The overall duration of the "calculable CW" mode is, for example, N seconds which are distributed before and after the splice point Ps at the instant T _s . One possibility is to take N equal to 3 crypto-periods CP.

These steps also apply in the case where the same value is used for the even control word and the odd control word.

At the local splicer-scrambler, the method executes, for example, the following steps:

X CP before the marked slicing point, we pass the scrambling of the local stream in "calculable CW" mode, with X = 2, for example,

the ES packets are scrambled with the calculated CW control word (respecting the parity switchover at each cryptoperiod change),

ECM ₂ carrying the predefined CW control word is generated at the local stream,

the step of stalling the national stream to the local stream is executed, then the ECMs of the national stream F are filtered out and the ECMs ₂ of the local stream F ₂ are broadcast on the same PID packet identifier as the ECMs of the national stream, and then ,

at the next crypto-period CP + 1, one goes into "random CW" mode in order to encrypt the local stream F ₂ for the rest of its broadcast.

To manage the return on the national stream, the method will perform the following steps:

• at the level of the national scrambler: the diffusion of the SCTE35 tables, in this example of implementation or any means for locating the splicing point, T _s2 , switching the scrambling mode "random CW" mode "CW calculable" according to a duration identical to that of the splice (one uses the mode "computable CW" on the duration of the splice),

after 3 CP (for example) in "calculable CW" mode, one switches to "random CW" mode in order to encrypt the national stream according to a known method and to continue broadcasting this encrypted stream;

at the local splicer-scrambler:

2 CP before the splicing point marked T _s2 , for example via the SCTE35 tables of the national stream, or by any other means, we go from the scrambling of the local stream from the "CW random" mode to the "CW computable" mode, on continues to disseminate local ECMs, and continues to filter ECMs from the national stream, and then

after the splice, the ECM filtering of the national stream is stopped and the local ECMs are stopped.

Two splicings are carried out in the process according to the invention. The first splicing concerns the audio / video splicing that is performed on the packets containing the beginnings of images and audio frames.

It consists, in particular, of:

- delete certain audio or image frames or in English "Access Unit" and thereby associated transport packages,

- modify the PTS / DTS and PCR packets to ensure clock continuity despite splicing, while taking into account the drift of the input clocks,

- modify the audio / video PIDs of the local to be the same as those of the national,

- change the headers of the video packets to the transition to ensure continuity in the decoding => this will sometimes involve having to create packages if the size of the headers is increased. This method will not work in the special case of CAVLC in H.264 (a case rarely used in H.264). The second splicing is that of ECM and EMM. The local stream being scrambled, we switch the ECM PID from the national to the local by "remapping" the output PID to ensure that there is a single ECM PID output splicer; in this case also the descriptors of the accessibility conditions or in English "CA_descriptors" are therefore always present and unchanged in the signaling (abbreviated PMT of program map table).

If the national flow F carries EMMs, the splicer lets them pass; CAT is unchanged (presence of CA_descriptors referencing EMM).

The method according to the invention advantageously makes it possible to work on scrambled flows and not have to decode them during normal operation of the process.

Claims

1 - Method for effecting the stall or "splicing" at a first instant T _S i in a system diffusing at least a first scrambled stream F _e by means of a first control word CW and at least a second scrambled stream F _2e by a control word CW ₂ characterized in that it uses the same value CW of the fixed control word to scramble simultaneously and during the duration of the splicing, at least partially the first flux F and at least partially the second flux F ₂ , the control word CW being fixed during the stall duration Ts of the first stream to the second stream and in that within a given time after the stall time T _S i broadcast ECM messages ₂ associated with the second stream F ₂ .

2 - Process according to claim 1 characterized in that the value of the control word CW is determined by means of an algorithm common to the scrambling device of the first stream F and the scrambling device of the second stream F ₂ .

3 - Process according to claim 1 characterized in that the CW value of the control word is determined from a table storing for a given moment, a control word value, the control word generator using said table M for partially scrambling the first stream F and partially scrambling the second stream F ₂ , for splicing.

4 - Process according to claim 1 for the stall of a first stream F to a second stream F ₂ characterized in that it comprises at least the following steps:

· At least partially scrambling the packets of the first stream Fi to broadcast, using a first key CW- ,,

Determining a first stall point at the time of stalling T _s i and triggering Ti seconds before this point a scrambling mode using a fixed control word CW, in order to partially scramble the first stream F _; · Transmit the stall point information at the stall time T _s i at the second stream F ₂ ,

• T ₂ seconds before the stall point at the time of stall T _s -i, at least partially scramble the flow F ₂ with the calculated CW fixed control word, after the stall point at the time of stall TVi, stop the broadcast ECMi control messages associated with the first stream Fi and broadcast the ECM messages ₂ associated with the second stream F ₂ using the same PID packet indicator that the indicator used for the ECM1 messages of the first F- stream,.

5 - Process according to claim 4 characterized in that the stall point T _s is determined from tables SCTE35 diffused with the first stream F to the device generating the second stream F ₂ . 6 - Method according to one of claims 4 and 5 characterized in that the first stream Fi is a national stream, the second stream F ₂ is a stream comprising a local program or an advertising program.

7 - Method according to one of claims 4 to 6 characterized in that one chooses for T _s whole values of crypto-periods.

8 - Method according to one of claims 4 to 6 characterized in that the first stream and the second stream being audio / video streams, it achieves the stall on packets containing the beginnings of images and audio frames.

9 - system for performing the stall or "splicing" at a first instant T _S i in a system diffusing at least a first scrambled stream F _e by means of a first control word CW and a first scrambler (3) and at least a second scrambled stream F _2e by a second control word CW ₂ and a second scrambler (10) characterized in that it comprises at least the following elements:

A controller (15) adapted to manage the ECM messages associated with the first stream F-, and ECM ₂ associated with the second stream F ₂ . 10 - System according to claim 9 characterized in that it comprises an algorithm adapted to generate one or more same CW fixed control word (s) to scramble the first stream F and to scramble the second stream F ₂ during a duration corresponding to the duration of splice.

1 1 - System according to claim 9 characterized in that it comprises a table M storing pairs formed by the value of a control word and a splice instant Ts.