Method and device for securing transmission, recording and viewing of digital audiovisual packet flows

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METHOD AND DEVICE FOR SECURING THE

TRANSMISSION, RECORDING AND VIEWING OF

DIGITAL AUDIOVISUAL PACKAGING STREAMS

The present invention relates to the field of processing digital audiovisual streams.

It is proposed in the present invention to provide a method and a system making it possible to recompose a digital audiovisual content previously modified visually.

The present invention relates more particularly to a device capable of securely transmitting a set of films of high visual quality to a display screen type television screen and / or to be recorded on the hard disk or on any other media. recording of a box connecting the remote transmission network to the display screen such as a television screen, a projector or a personal computer monitor, while preserving the audiovisual quality but avoiding any fraudulent use such as the possibility of making pirated copies of films or audiovisual programs recorded on the hard disk or any other recording medium of the set-top box.

The invention relates to a client-server system and the synchronization mechanism between the server which provides the secure digital stream for viewing audiovisual content and the client which plays and displays the digital audiovisual stream.

With current solutions, it is possible to transmit films and audiovisual programs in digital form via broadcasting networks such as terrestrial, cable, satellite, etc. or via DSL (Digital Subscriber Line) or BLR (radio local loop) type telecommunications networks or via DAB (Digital Audio Broadcasting) networks, etc. Moreover, to avoid pirating of the works thus distributed, the latter are often encrypted or scrambled by various means well known to those skilled in the art.

In the previous state of the art, the solution closest to our invention is described by document WO 00/60846 (Diva Systems Corporation). This prior art provides a Video on Demand distribution solution via a distributed server system. The protection of digital video content is based on an encryption system based on digital keys. The main innovation of this previous art is to allow an encryption and a decryption of the streams conforming to the MPEG-TS standard (MPEG-Transport Stream), simplified in that we first carry out an analysis of the MPEG stream in order to optimize the encryption according to the structure of the stream. The calculation time is in fact greatly reduced thanks to a selective and optimal encryption of the MPEG-TS stream. This stream analysis consists mainly in marking the TS packets containing information essential for correct decoding of the video, in the MPEG sense, so that in a second encryption phase, only the payload data of the marked TS packets are encrypted. Thus, the essential information is not available for unauthorized decoding, and the stream cannot therefore be displayed, while maintaining a reasonable computation time for the encryption. However, this solution does not make it possible to solve the security problem because the protection of the video stream is based on an encryption system based on digital keys, but for which the video stream transmitted to a receiving device contains, in an encrypted form, all the information initially present in the original video stream. Thus, the video stream received by the client equipment already contains all the information initially present in the unencrypted video stream, even if they are stored in a form which does not allow their immediate use. A malicious user, while being disconnected from the network, can process the encrypted video stream so as to put it back in a form usable by a conventional video decoder and can thus bypass the protection system.

The present invention relates to the general principle of a method for securing an audiovisual stream. The objective is to authorize video on demand and on demand services through all broadcasting networks and local recording in the memory of the user's digital set-top box, as well as live or online viewing. deferred, TV channels. The solution consists in keeping permanently outside the user's home, in fact in the broadcast and transmission network, part of the audiovisual program recorded at the user's home or broadcast live, this part being essential for viewing said audiovisual program on a television or monitor type screen, but being of a very low volume compared to the total volume of the digital audiovisual program recorded at the user's premises or received in real time. The missing part will be transmitted in real time via the broadcasting network (transmission) when the said audiovisual program is viewed.

Most of the audiovisual stream, called “modified main stream” will therefore be transmitted via a conventional broadcasting network while the missing part called “additional information” will be sent on demand via a narrowband telecommunications network such as conventional telephone networks. or cellular networks such as GSM, GPRS or UMTS or using a small part of a network such as DSL or BLR, or by using a subset of the bandwidth shared on a wired network. The audiovisual stream is reconstituted on the destination equipment (decoder) by a synthesis module from the modified main stream and the additional information.

Currently, the majority of security systems operate either on elementary Audio / Video elementary streams (ES: “Elementary Stream”), or directly on transport streams (TS: “Transport Stream”). The integration of its protection systems in the chain decoders (Satellite or Terrestrial), commonly called "Set-Top-Box" in English, poses certain problems linked to the very architecture of these decoders and the way in which they are used. process the data. In fact, the majority of 15-channel decoders use an intermediate format called PES (“Packetized Elementary Stream”), for processing and viewing data.

The present invention provides a protection system, comprising an analysis and scrambling module based on the PES format and respectively an analysis and descrambling module, and which is therefore easily integrated into existing digital audiovisual stream decoders. .

In its most general acceptance, the present invention relates to a method for the secure distribution of original digitized audiovisual streams made up of audio, video or other data components, characterized in that said original stream is a stream packaged in logical entities, called packets. , manipulable and of adjustable size, each packet comprising a header containing information on said packet and a payload comprising part of the data of the stream, and in that, before transmission to the client equipment, an analysis of said packaged flow is carried out to generate a main flow conforming to the packaged format of the original flow, modified in that all or part of said packets constituting it have been substituted by packets of the same structure but whose content has been modified, and additional information of any format, capable of allowing the reconstruction of said original stream, then in separately transmitting said modified main stream of additional information thus generated and said from the server to the destination equipment.

Advantageously, the method according to

The invention has the following specific characteristics:

• the substituted packets contain information relating to one or more audio or video streams included in the packaged stream • the analysis of the stream includes a step of selecting the packets to be substituted • each packet incorporates all or part of one or more units ( s) access • the complementary information contains the substituted packets from the original nominal flow • the complementary information contains the packets representing said access units • the complementary information further includes synchronization data containing time references and metadata associated with the modified or substituted packets • the additional information further includes instructions describing actions to be performed on the packets following the processed packet • the packets used to substitute the packets of the original stream are chosen so that said modified main stream has the same size in bytes as the original stream • we calculate on the equipment recipient a synthesis of a stream in nominal format as a function of said modified main stream and said additional information • the original stream to be protected is encoded according to any standard or any proprietary standard supporting the packaged format, such as for example the PES formats of standards MPEG-2 or MPEG-4.

The invention also relates to equipment for manufacturing an audiovisual stream comprising at least one multimedia server containing the original audiovisual sequences and a device for analyzing the audiovisual stream originating from said server in order to generate said modified main stream and said additional information.

According to the variants of this invention,

1¹ equipment further comprises a standard packaged stream player, at least one recording interface (hard disk) intended primary modified, in the packaged format and storing the content of said stream minus a decoder element processing at least one display interface and d 'hearing, characterized in that it comprises a means for recomposing the original stream from said modified main stream and from said additional information.

The invention also relates to a system for the transmission of an audiovisual stream comprising an audiovisual stream production equipment and at least one audiovisual stream operating equipment and at least one communication network between the audio-visual stream equipment. production and operating equipment (s).

The present invention will be better understood on reading the description of a non-limiting example of embodiment which follows, with reference to the figure which describes the overall architecture of a system for the implementation of the method according to invention. The development of the protection of the video and audio streams is based on the packaged structure of the audiovisual streams and the characteristics which result from this packageization, the properties of which we recall below using an example describing the PES format.

A PES (“Packetized Elementary Stream”) packaged elementary video stream is an infinite series of digitally encoded images (frames, planes), which can be of intra (reference I image), predicted (P images) or bidirectional (P images) type. B), as described for example in MPEG formats. Likewise, an elementary packaged audio stream is a series of audio frames or blocks. These coded video or audio frames are of different sizes and constitute what is

<td colspan="7">calls Access Units.</td>

<td></td><td>Before'</td><td colspan="2">to be transformed into</td><td>a</td><td>program flow</td><td>PS</td>

<td> («</td><td colspan="2">Program Stream ”) or</td><td>a</td><td colspan="2">transport stream</td><td>TS</td>

<td> («</td><td>Transport</td><td>Stream "),</td><td>a</td><td colspan="2">elementary flow</td><td>ES</td>

<td> («</td><td>Elementary</td><td colspan="2">Stream ”) undergoes</td><td>a</td><td colspan="2">intermediate stage</td>

<td colspan="2">packaging,</td><td>allowing</td><td>of</td><td>the</td><td colspan="2">cut into bundles</td>

useful and easily manipulated so called PES packages. The resulting flow is called the Packaged Elementary Flow (PES).

A PES packet of a packed elementary stream is a logical structure made up of a header and a payload. The payload simply represents the data taken directly from the access units of the elementary stream to be packaged. The start of the payload does not have to coincide with the start of an access unit, therefore an access unit can appear anywhere in the PES packet and it is even possible for multiple units to appear. access are contained in a single package.

The header of a PES packet can be of variable length, and mainly comprises a start of packet prefix, which, as its name suggests, allows synchronization with the start of a PES packet. This prefix is ​​followed by a stream identifier, which makes it possible to distinguish, in the same program, packets belonging to different elementary streams. The header can also contain timestamps, which are of two types. The PTS presentation timestamp ("Presentation Time Stamp") which specifies the time at which an access unit should be displayed and the DTS ("Decoding Time Stamp") decoding timestamp which specifies the time at which an access unit is to be displayed. The time at which an access unit must be moved from the storage buffer to the decoder for processing. In the case of PES audio packets, only the PTS timestamp is present, the audio frames being decoded one after the other. These two time stamps are of great importance and allow, among other things, to distinguish a PES packet in a unique way in the stream.

The size of a PES packet can be of variable size and this characteristic gives the flow great flexibility because the length of the PES packets can be modeled according to the intended application.

The analysis and scrambling system proposed by the present invention is based on the substitution and modification of PES packets. Indeed, as each PES packet contains part of an access unit or several access units, it is easy to remove a certain number of essential packets from the original flow and to replace them with replacement packets which ίο serve as decoys. Replacement packages have the same format as substituted packages. Before proceeding with a substitution of the packets, they are identified in a unique way, which allows their easy reconstitution. For example, the MPEG-2 Audio / Video standard in its system part (ISO / IEC 13818-1) specifies a certain number of elements which allow this identification. Thus, in the procedure described by the present invention, each PES packet to be substituted is uniquely identified by a pair composed of a stream identifier and either the presentation time stamp (PTS) in the case where the unit access that the said PES packet includes is of type I or P, or the decoding time stamp (DTS) in the case where the access unit that the said PES packet includes is of type B. For audio type packets, the same principle is applied so that each audio packet in PES format is identified by the identifier of the stream to which it belongs and by the presentation time stamp (PTS) of the audio access unit. associated with it. Concretely, the scrambling system receives as input an elementary stream (ES) or a transport stream (TS), transforms it into PES format and after analysis of the content of the PES packets, produces two different streams, a modified main stream which contains the original stream in which a certain number of PES packets have been replaced by "decoy" packets, and additional information which contains the packets with the original values ​​and optionally, the information needed to locate these packets in the PES stream and / or instructions for making modifications in the packets following the modified packet. The packets to be substituted are judiciously chosen to guarantee a reasonable rate of the complementary information. Also, for example, a compromise is made between the degree of visual scrambling, and the volume or rate of the complementary information at the output of the analysis and scrambling module. The original stream is reconstituted in the decoder box of the destination equipment in which the analysis / descrambling module is integrated, which, depending on the modified main stream and the additional information sent in real time, reconstitutes a stream strictly identical to the stream. original PES. The process is lossless.

The invention will be better understood on reading an exemplary embodiment relating to a stream in MPEG-2 format. In this example, the invention demonstrates the integration of a descrambling module in a channel decoder (Satellite or Terrestrial) on the market. This analysis / descrambling system is the counterpart of the analysis and scrambling system detailed above, because it performs the reverse operation of the latter. It shows how well the choice of packaged elementary stream is suitable for processing in hardware platforms. In this preferred embodiment, but not limited to, element (1) is the video stream to be scrambled, module (2) is the analysis and scrambling module which receives as input an audiovisual stream in MPEG format. 2 TS or MPEG-2 ES, transforms said input stream into an MPEG-2 stream in PES format and generates two different parts at its output: the modified main stream, reconverted into TS format (31) after the substitution of certain PES packets, and the additional information (51) of any format. The modified main stream (31) is stored in the buffer (3) of the server (4), then is sent in real time to the user via a high-speed network (7) which may for example be of the ADSL, cable or satellite. The additional information (51) is stored in the buffer (5), then is sent to the destination equipment (20) via a low-speed transmission means (6) such as a conventional telephone line, or GSM or GPRS mobile networks, UMTS, or a wired or wireless local loop network. The networks (6) and (7) can be combined into a single network, for example the additional information (51) is also sent via a broadband network (7).

The element (20) represents a set-top box for a satellite channel for example. The modified main stream (31) in MPEG-2 TS format arrives directly at the input interface (17) and passes through the bus (11) to the demultiplexer (12). The demultiplexer (12) generates a packaged elementary stream (PES) and sends it back to the data bus (11) to be processed and / or stored. In another embodiment, the main stream modified at the input of the demultiplexer (12) comes from the hard disk (13) of the decoder box. According to one variant, the modified main stream (31) arriving at the input interface (17) comes from an external hard disk (15) such as for example the hard disk of a PC connected to the decoder box (20). In another embodiment, the main stream modified at the input of the interface (17), comes from a physical medium (CD, DVD or other storage element) (71) burned at the output of the server (4) with the information of the main stream modified (31) and transmitted to an external reader (18). Advantageously, the physical medium (71) is read by a reader (16) integrated in the housing (20).

In another exemplary embodiment, the modified main stream is first processed by the demultiplexer (12) and then stored in PES format in the hard disk (13) of the decoder box. Advantageously, the modified main stream is previously stored in TS format either on a hard disk (that of the decoder box (13) or an external hard disk (15)) or on a physical medium (CD, DVD) before being de- multiplex.

In order to perform descrambling, the modified main stream is sent in PES format to the temporary storage memory (10) via the transport bus (11). The additional information (51) is then transmitted on demand to the decoder box (20) via the network (6) and after having passed through the input interface (17) and the data bus (11), is stored. partly in the temporary storage memory (10).

The synthesis and descrambling device (8) recovers the parts of the modified main stream (31) and of the additional information (51) stored in the temporary storage module (10) and performs real-time descrambling of the modified main stream . The additional information (51) arrives in real time via the network (6), the input interface (17) and the bus (11) as and when the synthesis device (8) needs it. However, all of the additional information (51) is never sent in full to the user. Once the stream has been descrambled, the synthesis device (8) sends it to the reader (9), which decodes it and then sends it to a viewing and hearing module (14) of the television screen type.

Let us now describe another exemplary embodiment by detailing the different steps for a user (20).

The portal (4) has chosen the MPEG-2 TS stream (31) that it must send to the user's decoder box (20) to be viewed on his television screen (14). This user is connected to a digital broadcasting network (7) and to an ADSL telecommunications network (6).

The analysis and scrambling module (2) of the portal (4) therefore reads the incoming MPEG-2 TS (1) or MPEG-2 ES (1) stream, transforms it into an MPEG-2 PES stream, analyzes the content of PES packets and each time it detects a PES packet to be modified, substitutes it with a “decoy” PES packet, which is the same size as the substituted video and audio packet. Unlike audio whose frames are chosen of constant length, for video, this analysis allows it to recognize in the bitstream the access units to be modified according to what they contain: I, P frames or B. The choice of PES packets to be modified is made as a function of the bandwidth available for the additional information (51). If the link (6) is of low speed, PES packets containing access units comprising B or P images are substituted, and if the link (6) is of higher speed, certain access units are also substituted. containing images I. The content of the PES packets is substituted by random values ​​without changing their size, within the PES packet, in order to make the frames (and therefore the sequence) unacceptable from the point of view of human visual and auditory perception but fully compliant. to the standard of the input stream format (1). The real PES packets are stored in the output buffer (5), which will later allow the reconstitution of the starting sequence in the box (20), following the reverse scheme.

The analysis and scrambling module (2) then writes each real PES packet in the buffer (5) and continues its analysis until the end of the MPEG-2 input stream, in order to select the next PES packets to be edit. According to a variant of this example, the analysis and scrambling module (2) also writes in the buffer containing the complementary information (51) information making it possible to locate the modified packet in the PES stream.

According to another variant, the analysis and scrambling module (2) furthermore writes in the buffer containing the complementary information (51) of the instructions and of the data describing modifications to be carried out on the PES packets which follow the substituted packet. .

The new modified MPEG-2 stream is then converted into MPEG-2 TS format to be broadcast on the broadcast network through the link (7) and recorded in the output buffer (3). The substituted PES packets of the incoming MPEG-2 stream (1) are stored in the buffer (5) of the portal (4). Advantageously, the new modified MPEG-2 stream is converted into MPEG-2 TS format in order to be recorded on a disc (71) of CD or DVD type. The CD or DVD (71) thus created will be read when the stream is displayed, by the decoder (20) via the internal reader (16) or via the external reader (18).

At the same time or later, and for example in a completely unsynchronized manner, the modified MPEG-2 TS output stream coming from the output buffer (3) of the portal (4) is broadcast via the broadband network (7) to the input interface (17) of the user (20), and stored, after demultiplexing, on the hard disk (13) of the set-top box in PES format. Advantageously, the protected MPEG-2 stream is broadcast to a set of users (20).

The phase described above corresponds to the first phase of preparing the MPEG-2 stream by the portal (4), its transmission via the broadband network (7) and its recording in a decoder (20). This decoder can then, after processing, display this MPEG-2 PES stream recorded on its hard disk (13). For this, the synthesis system (8) of the decoder (20) reads the MPEG-2 PES file from its hard disk (13), and sends it to a conventional MPEG-2 player (9). If no additional information is received by the synthesis system (8), then the MPEG-2 PES stream which reaches the reader (9) is processed, displayed and listened to as it is, which causes significant distortion of the sound and of the sound. the display on the television (14). Indeed, the modified PES packets which are processed by the synthesis module (8) do not correspond to the PES packets which are necessary for correct viewing and hearing, since some of these PES packets have been replaced by packets with random values. . On the other hand, as the recorded stream is indeed an MPEG-2 PES type stream, the reader (9) makes no difference and restores the information on the output screen (14) which does appear to be data from a stream. MPEG-2 PES audio / video but completely inconsistent for the eye and the ear of the human being who looks at the television screen (14) and listens to the sound. Any copy of the MPEG-2 TS stream coming from the hard disk (13) of the box (20) will produce the same audiovisual effect when it is restored by any MPEG-2 player. When the user of the decoder (20) really wants to view on his screen (14) the audiovisual program recorded on his hard disk (13), he requests it from the synthesis system (8) with his remote control as he would with a VCR or DVD player with a menu on its television screen. The synthesis module (8) then makes a request to the hard disk (13) and the data read is temporarily stored in the input buffer (10). The synthesis module (8) then establishes a link with the portal (4) via the telecommunications network (6) which is in our example an ADSL link. Once this link is established, and throughout the viewing period of the film or audiovisual program, the synthesis module (8) sends the original PES packets from the buffer memory (5) of the server (4) through the buffer ( 10) where the demultiplexed PES stream is temporarily recorded. These data reach the synthesis module (8) via the internal bus to the decoder (11). The synthesis module (8) identifies the packets to be modified using the location data contained in the complementary information (51).

According to one variant, the PES packets are read and their location in the stream is obtained by reading their header.

According to another embodiment, the complementary information contains, in addition to the original PES packets, instructions on actions to be carried out on the packets to be followed, for example inversion of certain well-selected bits in a part of the packets which follow. From the modified MPEG-2 PES stream which also arrives from the buffer (10) and from the original PES packets which arrive via the link (6), the synthesis module (8) reconstructs in an inverse manner to the analysis process and scrambling described above, the original MPEG-2 PES stream and sends the MPEG-2 PES stream thus reconstituted to the player (9) to be displayed on the screen (14) and played correctly.

Advantageously, as soon as they are used, the original PES packets coming from the portal (4) constituting said additional information (5) are deleted from the synthesis system (8).

Advantageously, before the portal (4) sends the original PES packets and associated data from its buffer (5), the portal (4) has verified that the user of the box (20) was indeed authorized to receive said information. complementary.

Advantageously, the modified main stream (5) is passed directly via a network (7) to the input interface (17), then is passed through the bus (11) to the buffer memory (10) and the control module. synthesis (8).

Advantageously, the modified main stream (31) is written (recorded) on a physical medium such as a disk of CD-ROM, DVD, hard disk, flash memory card, etc. (71). The modified main stream (31) will then be read from the physical medium (71) by the disk drive (16) of the box (20) or else by the external disk drive (18) to be transmitted to the read buffer memory (10) then to the synthesis module (8).

Advantageously, the additional information (51) is recorded on a physical medium (52) of credit card format, consisting of a chip card or a flash memory card. This card (52) will be read by the module (17) of the device (20) which comprises a card reader (61).

Advantageously, the card (52) contains the applications and the algorithms which will be executed by the synthesis module (20).

Advantageously, the device (20) is an autonomous, portable and mobile system.

This preferred exemplary embodiment applies to audiovisual streams originating from the MPEG-2 standard and also to all normalized or standardized digital formats such as MPEG-1, MPEG-4, H262, H264, as well as to digital formats generating packets of private data, that is to say that the securing process applies to all digital formats, for example, but not only, to those regulated by the “Systems” part of the MPEG-2 standard (ISO / CEI 13818 -1).