Abstract:
The application relates to a method for distributing a marked audiovisual sequence from a nominal audiovisual sequence, said nominal audiovisual sequence having a nominal content, wherein
       a first modified flow having a modified content different from the nominal content is generated, and   a second marked complementary flow including marked complementary digital information is generated;   said first modified flow and said marked complementary information are transmitted, so as to allow the restoration of said marked audiovisual sequence at the receiving item of equipment;   an operation of marking said nominal audiovisual sequence is carried out, so as to determine a marked audiovisual sequence having a marked content;   a difference is determined between said marked content, on the one hand, and said modified content or said nominal content, on the other hand;
 
wherein said marked complementary digital information depend on said difference.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Phase Entry of International Application No. PCT/FR2007/001999, filed Dec. 5, 2007, which claims priority to French Patent Application No. 06/55315, filed Dec. 5, 2006, both of which are incorporated herein by reference. 
     BACKGROUND AND SUMMARY 
     The invention relates to a method for distributing audiovisual sequences. 
     In order to protect an audiovisual sequence against hacking, it is known to tattoo the audiovisual sequence in a visible or invisible way, so as to identify the holder of a pirated copy. It is also known to encipher the audiovisual sequence during a transmission in order to prevent the illegal playing of the sequence. Of course, it is possible to combine the two protection methods by enciphering the audiovisual sequence at the level of an enciphering module on the transmitting side and by tattooing the sequence after the deciphering at the level of a tattooing module on the receiving side. However, such a method would not prevent a fraudor from retrieving the sequence at the output of the deciphering module prior to the passage thereof at the tattooing module. Such a fraudor could then freely use the non tattooed audiovisual sequence if he or she could decipher the sequence. 
     In order to solve this general problem, a method is known for distributing a marked audiovisual sequence from a nominal audiovisual sequence to a receiving item of equipment, said nominal audiovisual sequence having a nominal content, the method including steps wherein:
         a first modified flow having a modified content different from the nominal content is generated, and   a second marked complementary flow including marked complementary digital information is generated;   said first modified flow and said marked complementary information are transmitted to the receiving item of equipment so as to allow the restoration of said marked audiovisual sequence at the receiving item of equipment.       

     Such a method is known from the application WO 2004/062281. In one embodiment of this application, the complementary flow includes marking instructions intended to insert an invisible and customized mark into the marked audiovisual sequence. In a preferred embodiment of the application WO 2004/062281, these instructions more particularly make it possible to reverse the LSB of some visual coefficients, such as the DC coefficients. The absence or not of a reversion on an LSB will make it possible to determine the first mark inserted into the audiovisual sequence during an identification step. With such instructions being inserted into the complementary flow, a fraudor could not have access to the audiovisual content prior to the application of the marking instructions and thus prior to the insertion of the first customized mark. 
     However, this type of method cannot be used in combination with known tattooing or marking devices. As a matter of fact, in the above-mentioned application, the elements contained in the marked complementary information enabling the marking of said audiovisual sequence contain instructions which are specific to the marking operation: reversion of the LSB of some visual coefficients. Marking instructions are thus predefined so that it is not possible to mark the audiovisual sequence using a standard marking device thus generating a priori unknown marking information. 
     Following the above-mentioned document, a problem that the invention intends to solve is thus to facilitate the marking of the audiovisual sequence. Another problem which the invention intends to remedy consists in allowing the marking of an audiovisual sequence while allowing the utilization of any type of marking device or without knowing the marking information beforehand. Such problems are solved by the invention which relates to a method such as described hereabove, wherein the step during which the second mark complementary flow is generated, includes steps wherein:
         an operation of marking of said nominal audiovisual sequence is carried out so as to determine a marked audiovisual sequence having a marked content;   a difference between the marked content, on the one hand, and said modified content or said nominal content, on the other hand, is determined; said marked complementary digital information depending on said difference.       

     Thus, according to the invention, using the difference between, on the one hand, the marked content and the modified content or the nominal content, on the other hand, it is possible to determine what mark has been applied to the nominal audiovisual sequence during the marking operation, while transmitting data enabling the restoration of the marked audiovisual sequence in a secure way. Thus, it is possible to transmit one securely marked audiovisual sequence without knowing a priori the marking information and thus from any tattooing device. 
     According to one embodiment of the invention, the step consisting in determining a difference between said nominal content and said modified content includes steps wherein:
         a second modified complementary flow comprising complementary digital information capable of allowing the restoration of the nominal content from the modified content is generated,   at least a piece of marking information is determined as a function of the bit differences between the marked content and the nominal content;   said marked complementary digital information are determined as a function of said complementary information and said marking information.
 
This embodiment has the advantage of being implemented on a known protection module. In this embodiment, said marking information, said complementary information and said marked complementary information can have an identical format. This more particularly makes it possible to make the transmission method even safer.
       

     Besides, in one embodiment, the step consisting in generating said second marked complementary flow includes steps wherein:
         a second modified complementary flow comprising complementary digital information capable of allowing the restoration of the nominal content from the modified content is generated,   marking information are determined so as to enable the restoration of said marked audiovisual sequence from said nominal audiovisual sequence, said marking information being determined further to the operation of marking said nominal audiovisual sequence;   said marked complementary digital information are determined as a function of said complementary information and said marking information, wherein said marking information, said complementary information and said marked complementary information have an identical format.
 
According to another embodiment of the invention, the step consisting in determining a difference between said marked content and said modified content includes steps wherein:
   said marked content and said modified content are compared at the bit level so as to determine said difference.
 
This more particularly makes it possible to easily obtain the difference between the marked content and the modified content.
       

     In order to obtain a marked audiovisual sequence which is also customized, said marked complementary information may include a customization identifier. This customization identifier can include a single identifier of said receiving item of equipment and/or a single identifier of a user of said receiving item of equipment, and/or a single identifier of said marking operation. This makes it a customization of the marked content possible as a function of the selected identifier and by possibly using an identifier database. The marking according to the invention can thus include a tattooing and a customization. 
     In order to improve the protection of the audiovisual sequence against possible fraudors, said marked complementary digital information can include information relating to digital rights associated with the nominal audiovisual sequence. Said marked complementary information include a tattoo so that said marked content is visually and aurally identical to the nominal content, so that possible fraudors will not be able to detect the marking and so that an authorized user will not be disturbed in the consumption of said marked audiovisual sequence. Said nominal audiovisual sequence has a nominal format wherein said modified content has a format identical with said nominal format, so that a user can have access to some information of the nominal audiovisual sequence without being able to consume this sequence in a satisfactory way without a particular authorization. 
     The invention also relates to a system for distributing a marked audiovisual sequence from a nominal audiovisual sequence to a receiving item of equipment, said nominal audiovisual sequence having a nominal content, 
     the system including: 
     
         
         
           
             means capable of generating a first modified flow having a modified content different from the nominal content, and 
             means capable of generating a second marked complementary flow including marked complementary digital information; 
             means capable of transmitting to the receiving item of equipment said first modified flow and the marked complementary information, so as to allow the restoration of said marked audiovisual sequence at the level of the receiving item of equipment;
 
the system being characterised in that the means for generating a second marked complementary flow include:
 
             means capable of carrying out an operation of marking said nominal audiovisual sequence so as to determine the marked audiovisual sequence having a marked content; 
             means capable of determining a difference between, on the one hand, said marked content and on the other hand, said modified content or said nominal content; 
             means capable of generating said marked complementary digital information as a function of said difference. 
           
         
       
    
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Several embodiments of the invention will now be described while referring to the appended Figures wherein: 
         FIG. 1  illustrates the global architecture of a system for the implementation of a method according to a first embodiment of the invention; 
         FIG. 2  illustrates the global architecture of a system for implementing a method according to a second embodiment of the invention; and 
         FIG. 3  illustrates the global architecture of a system for implementing a method according to a third embodiment of the invention. 
     
    
    
     In the Figures, identical references refer to similar technical elements except otherwise indicated hereinunder. 
     DETAILED DESCRIPTION 
     An embodiment of the invention will now be described while referring to the appended  FIG. 1  which illustrates the global architecture of a system for implementing the method according to the invention. In  FIG. 1 , an audiovisual content  1  undergoes two main operations in a server equipment  14 . The initial digital audiovisual flow  1  is sent to an analyzing device  2  which uses the characteristics of the audiovisual encoding format of the initial audiovisual flow  1  to determine a modified main flow  101  and complementary digital information  102 . The modified main flow  101  has the same format as the initial flow  1  but underwent some modifications in certain parameters, thus being legible on a standard player of this format, but the display of the corresponding audiovisual content is not correct as regards human perception. In the case of the digital audiovisual standard MPEG, the modifications brought to the initial flow  1  can be: a substitution of some DCT coefficients in certain blocks, a substitution of information on the movement compensation, a substitution of the order of scanning the coefficients of some images, etc. In this case, the complementary information  102  thus extracted represent only about 1% of the data of the modified main flow  101  to jam almost totally, visually and/or aurally the original digital audiovisual flow  1 . 
     The modifications brought and the original information replaced, if any, in the modified main flow  101  are stored in the complementary digital information  102 . The complementary information  102  can thus include data (for example coefficients describing the original digital flow or extracts from the original flow) and functions (for example the substitution or permutation function). A function is defined as containing at least one instruction linking data and operators. The complementary digital information  102  describe the operations to be carried out to restore the original flow from the modified flow. 
     The complementary information  102  and the modified main flow  101  can be generated as in the application WO 2004/015996. 
     Within the scope of the second step of analysis, the initial audiovisual flow  1  is sent to a tattooing device  3  for determining a tattooed and customized audiovisual flow  106  with the information from a user managing system  4 . The customization information originating from the system  4  is supplied as an input to the tattooing device  3 . The tattooed audiovisual flow  106  is customized for each client or each transaction which includes the sending of information giving the client device  11  access to the content. 
     The retrieving device  5  determines tattooing information  112  by comparing the tattooed audiovisual flow  106  and the initial audiovisual flow  1  at the bit level. The tattooing information  112  contain the part of the tattooed audiovisual flow  106  which is different from the initial audiovisual flow  1 . The format of the tattooing information  112  is the same as that of the complementary information  102 . 
     The tattooing information  112  can include data (for example coefficients describing the original digital flow or extracts from the original flow) and functions (for example, the substitution or permutation function). A function is defined as containing at least one instruction linking data and operators. Said tattooing information describe the operations to be carried out for restoring the tattooed audiovisual flow from the original flow. The tattooing information can be customized for each transaction. When the tattooing information inserted into said original flow, the identification of the transaction is possible even though the restored flow is submitted to hacking attempts of the recoding or analogical capture types. 
     Tattooed complementary information  103  are determined by a composition device  6  by combining the tattooing information  112  with the complementary information  102 . The composition device  6  first copies the complementary information  102  into the tattooed complementary information  103 , then it inserts the tattooing information  112  into the tattooed complementary information  103 . In the case where the tattooing information  112  and the complementary information  102  contain references to the same part of the initial audiovisual content  1 , the data relating to said references in the complementary information  102  will be replaced with those of the tattooing information  112  in the tattooed complementary information  103 . 
     The tattooed complementary information  103  can include the assembly composed of the complementary information  102  and the tattooing information  112 . The digital format of the three types (complementary, tattooing and tattooed complementary) of information is identical, which makes it impossible to separate the complementary information  102  from the tattooing information  112 , when the tattooed complementary information  103  are generated. This functionality offers an important advantage: the separation of the two processes (that of restoring the original flow and that of the tattooing) becomes impossible, even for a client station comprised further to a successful hacking attempt. 
     The transmission of the tattooed complementary information  103  to the audiovisual decoder  11  is made secure by one of the protection systems  7  which is well known to the persons skilled in the art. Tattooed complementary information  103  are transmitted via the diffusion and transmission network  10  upon or prior to the viewing of said digital audiovisual program  1 , or the tattooed complementary information  103  are packed with the greatest part of the modified main flow  101  by the packing device  8  by being for example added to the complementary data or metadata of the file including the modified main flow  101 . A user having the receiving item of equipment  11  at home can play any audiovisual content originating from the telecommunication network  10  or originating from the physical media player  91 . When he or she wishes to view the modified audiovisual flow  101 , he or she cannot do it but by restoring the complementary digital information  102 . 
     A de-multiplexer  81  transmits, on the one hand, the modified main flow  101  to the buffer memory  104  and on the other hand, the tattooed complementary information  102  protected are sent to a de-protecting module  71  which is compatible with the protection system  7 . The de-protection module  71  transmits the tattooed complementary information  102  as a plaintext to a buffer memory  105  while respecting the restrictions imposed by the protection system  7 . A synthesis device  21  retrieves on the fly the tattooed audiovisual flow  106  from both buffer memories  104  and  105  containing the synchronized parts of the modified audiovisual flow  101  respectively of the tattooed complementary information  103 . The tattooed audiovisual flow  106  is identical with the modified audiovisual flow  101  as regards the audiovisual result, but it contains an invisible mark which can be detected by means well known to the persons skilled in the art. The tattooed audiovisual flow  106  is decoded by the audiovisual decoder  22  and it is rendered to the consumer using the rendering device  12 . Advantageously, the tattooed flow is sent to a recording module  13  to make a private copy of the content onto a physical medium such as a DVD, a CD or memory card. 
     The general principle of a securing method for an audiovisual flow is described hereinafter. The aim is to authorize the audiovisual on demand and pay per view services through all the diffusion networks and the local recording into the memory of the digital decoding box of the user, the decoding box  11  can be a decoder connected to a TV set, a personal computer of the PC or MAC types, a handheld terminal of a telephone or a personal assistant of the PDA type  12 . The solution consists in tattooing using one or several tattooing algorithms, the complementary information  102  which is represented by a small part of the audiovisual program  1 , this part being most important to listen to and/or view said audiovisual program  1  on a screen, but having a very small volume with respect to the total volume of the digital audiovisual program  1  which will be free for distribution and copying. 
     Said tattooed complementary information  103  of the audiovisual program  1  are composed of the complementary information  102  which enable the restoration of the original flow  1  from the modified flow  101 , and the tattooing information  112 , which make it possible to mark in an invisible and inaudible way the content, as well as the digital or analogical fraudulent copy of said a tattooed content  106  enable the traceability of the malevolent user by analyzing said tattooing information  112 . The modified main flow  101  is freely distributed to the users and between the users in a physical way on any storage medium  9  of the memory cards, CD, DVD, external peripheral unit types. The modified main flow  101  can be played on a conventional playing device  91  of this medium type, of the CD-ROM and/or DVD player, memory card player kinds. 
     According to an alternative solution, the modified main flow  101  is transmitted via a conventional telecommunication or diffusion network  10 . Tattooed complementary information  103  are sent upon request via a narrow band telecommunication network  10  such as the conventional telephone networks and or cellular networks such as the GSM, GPRS or UMTS types or by using a small part of a network of the DSL or BLR types or then by using a sub-assembly of the shared bandwidth on a wire or satellite network. Thus, the user never has the integral original audiovisual flow  1  in a non protected digital form on his or her equipment and thus cannot reproduce it in an illegal way. At worst, the user can have access to the de-protected, but tattooed, audiovisual content, which enables the traceability of the fraudulently distributed and used copies. 
     According to a particular embodiment, the consumption of an audiovisual content is submitted to digital rights. Digital rights represent the information which indicate the conditions under which the content can be consumed: (a) the number of the consumptions of the content, (b) the validity date from which the content can be used, (c) the expiration date from which the content can no longer be consumed, (d) other types of rights such as the domain for which the consumption is authorized, the type of the decoder  22  which enables the consumption, etc. Advantageously, digital rights on the consumption of the main digital flow are recorded by the protection system  7  in the protected tattooed complementary information  103  transmitted to the multiplexer  8 . Tattooed complementary information  103  as well as the modified main flow  101  can thus indifferently reach the receiving item of equipment  11 , together or separately, through the communication network  10  or via a physical medium  9  which is played by the player  91  of the receiving item of equipment  11 . 
     In a second exemplary embodiment referring to the appended  FIG. 2 , a tattooed audiovisual flow  111  is marked in a generic way, the customization of the tattooed flow which requires the connection to the users managing system  4  being postponed to the following step. In this second exemplary embodiment, the composition device  61  extends the functionality of the composition device  6  by providing an additional step applied prior to the execution of the functions of the composition device  6 , a step which consists in customizing the tattooed information  112  with information from a user managing system  4 . 
     In a third exemplary embodiment referring to the appended  FIG. 3 , the extraction device  5  determines tattooed complementary information  103  by comparing the tattooed audiovisual flow  106  and the modified main flow  101  at the bit level. Tattooed complementary information  103  contain the part of the tattooed audiovisual flow  106  which is different from the modified main flow  101 . 
     In the three above-mentioned embodiments, the tattooed audiovisual flow  106  which is restored at the level of the receiving item of equipment  11  is customized as a function of the receiving item of equipment  11 , one of the users thereof or one identifier of the tattooing operation, through the user managing system  4 . However, the invention can be implemented without this customization so long as the audiovisual content  1  is marked with identifiable information for example a tattoo.