Patent Publication Number: US-2012045054-A1

Title: Method and apparatus for delivering watermarked digital media content to a user upon request

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/366,232, filed Jul. 21, 2010, the entire contents of which are hereby incorporated by reference herein. 
    
    
     TECHNICAL DOMAIN 
     The present invention relates to methods and apparatus for embedding and for detecting user-specific watermarks or fingerprints in digital information signals. The invention alto relates to the field of adaptive streaming in the transmission of a digital information signal and is particularly targeted at an environment where the reception of such a transmission is requested, as in a pay per view TV environment for example. 
     STATE OF THE ART 
     United States Patent Application Publication Number US 2008/0010653 A1 discloses methods and apparatus for controlling access to and usage of digital information by use of watermarking techniques. Such watermarking techniques allow an owner of a transmitted digital media object such as audio-video content to apply control over unauthorised redistribution of copies of such transmitted content. The invention allows notably for redistributors of such content to be identified. The document discloses techniques which allow for an owner digital content to be able to trace a user who has requested a particular content and who has redistributed the content without authorisation. The technique involves the content owner storing the digital content with a number of predetermined portions of the content missing. The thus stored partial content can be either broadcast to a plurality of users or delivered to one or more users on request. Such users will therefore be able to consume the content at a somewhat reduced quality. In order to have access to a high quality version of the content, the user has to request the missing portions from the content owner. The content owner watermarks the missing portions using user-specific watermark information before delivering the watermarked missing portions to the user and the user-specific watermark information is stored by the content owner in this way, should the user attempt to redistribute the complete content without authorisation and should the content owner intercept a transmission of the redistributed content, then the content owner can identify the fraudulent user. 
     The method described in this publication is particularly appropriate for “luring” techniques, whereby a particular content is made available for consumption by users but at a somewhat degraded quality. By withholding certain portions of a content and allowing a user to consume the remaining content a user can be “lured” or otherwise encouraged into making a request for and paying for the missing portions so that he may enjoy the content at its full quality. Since the missing portions will be watermarked following the user&#39;s request for those portions, any attempt made by that user to pass on the complete content will be subject to detection. 
     Adaptive streaming techniques have been described in the state of the art relative to the transmission of digital information signals, such as audio-video content, especially in an environment where the transmission of such content is subject to constraints associated with a finite bandwidth allowed for such transmission or the processing power available using a given piece of viewing hardware/software. Adaptive streaming techniques involve the preparation and storage of a plurality of streams each representing the same content, each stream delivering the same content at a different bit-rate. Depending on the bandwidth available for the transmission or the capability of the equipment used by a user to make use of the transmission, the stream representing the content at a bit-rate which is appropriate for the transmission conditions and/or processing conditions at a particular time is used. As the transmission conditions or the processing conditions evolve, so the appropriate bit-rate can evolve i.e. different streams are selected for transmission depending on the evolving transmission/processing conditions, hence we speak of “adaptive streaming”. 
     International Patent Application Publication Number WO 2004/040913 A1 describes a method for embedding a watermark in an information signal, wherein the watermark embedding process is dependent on the bit-rate of the signal to be watermarked. One of the requirements of a watermark is that it should not reduce the quality of the signal which is watermarked. Another requirement, although conflicting with the first requirement is that the watermark should be robust in that it should not be easy to remove by a third party. The method described in this document allows for a good trade-off to be achieved whereby the robustness of the watermark is made to be adequate for a signal having a given bit-rate, while the degradation of the signal due to the watermark is kept to a minimum. This allows for watermarking to used in an adaptive streaming context for example. The watermark obtained using the process described in the document however is independent of the targeted user of the information signal and therefore does not as such allow for “fingerprinting” of a content which is made available to a particular user on demand. 
     BRIEF SUMMARY OF THE INVENTION 
     As is generally known in the state of the art, watermarking of digital content, whereby the content is coded or otherwise encrypted according to some unique identifying parameter associated with a requestor of such content, can lead to significant overheads whereby the watermarking process becomes costly in terms of processing power and transmission bandwidth as well as in terms of the treatment of such watermarked content at the reception end. It is a goal of the present invention to allow for the benefits associated with watermarking technology to be maintained (i.e. the tracing of a source of so-called content leak for example) while at the same time allowing for the drawbacks dire to the resulting increased overhead to be addressed. A particular content which is to be made available by a content provider to potential content users is prepared by encoding the content into a plurality of different encoded streams. Each of the encoded streams is prepared by encoding according to a different bit rate and comprises a plurality of chunks, each chunk individually retrievable by a requestor. Upon request of said content by a user, the chunks making up the content are selected from the plurality of the different encoded streams and a subset from that plurality of chunks is watermarked using a unique identifying parameter associated with the requestor, such as a unique address or a user ID or even a unique key associated with the requestor for example. It is to be understood that a stream may comprise separate elementary streams. For example an audio-video stream may comprise an audio elementary stream and a video elementary stream. 
     According to embodiments of the present invention there is provided a method for delivering on request, digital media content from a provider, to a user, said digital media content comprising a watermark relating said digital media content to said user, said method comprising:
         receiving from the user, via a first communication channel, a request for digital media content;   encoding said digital media content into a plurality of encoded streams, each of said encoded streams being encoded according to a different bit-rate each encoded stream comprising a plurality of chunks, the plurality of said chunks from one of said encoded streams allowing to reconstruct the digital media content;   selecting, by the provider, a set of chunks in a sequence allowing for reconstruction of the digital media content, said selection being made from said plurality of encoded streams;   selecting, by the provider, a subset from said set of chunks, thereby giving a subset of selected chunks and a subset of remaining chunks;   watermarking the subset of selected chunks, said watermark being bated on unique parameter associated with the user; and   delivering the watermarked set of chunks to the user, said watermarked set of chunks including the watermarked subset of selected chunks and the subset of remaining chunks.       

     There is also provided a content delivery system comprising:
         a content provider for storing digital media content;   at least one encoder for generating, from said stored digital media content; at least one stream of encoded content comprising a plurality of chunks;   a communication channel configured to receive, from a user, a request for the content;   a watermarking module to watermark at least one chunk, giving a watermarked content, said watermark being based on a unique parameter associated with the user; and   a delivery channel to deliver at least the watermarked content to the user, said delivery channel comprising at least the communication channel;   said content delivery system characterised in that:
           the encoder is configured to generate at least one further stream of encoded content, each of said streams of encoded content being encoded at a different bit-rate;   
           the content delivery system further characterised in that it further comprises
           a selection module to select a set of chunks from said streams of encoded content in a sequence allowing reconstruction of said digital media content; and   a filter to select a subset from the set of chunks and to send the subset to the watermarking module.   
               

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be better understood thanks to the detailed description which follows and the accompanying drawings, which are given as non-limiting examples of embodiments of the invention, namely: 
         FIG. 1 , representing a schematic of a device in which an embodiment of the present invention may be deployed; 
         FIG. 2 , representing a system comprising a content provider and a user connected to each other via a content delivery network, in which an embodiment of the present invention may be deployed. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present invention may be deployed in a content delivery system wherein a provider of digital media content, such as audio-video content for example, makes such content available to a user or a plurality of users upon request, usually for a fee. Such systems are known as video on demand systems. 
     The content provider may feel a need to protect the content he makes available to such a requestor from the possibility that the requestor then makes the content available to further users without the authorisation of the content provider, possibly resulting in a loss of potential revenue perceived by the content provider for such content. 
     According to an embodiment of the present invention, the content provider prepares a particular content with a view to transmitting, or otherwise making available for access, said prepared content upon request. Such preparation involves encoding or otherwise converting the content into a plurality of encoded or converted streams, each encoded stream comprising a plurality of chunks or segments. This is similar to adaptive streaming technology in that several encoded streams are prepared representing the same content, with each stream being encoded using a different bit-rate. The result according to the embodiment of the present invention is that a plurality of streams encoded at different bit-rates is prepared, each stream comprising a plurality of chunks. The plurality of differently-encoded streams may exist in a single file or as multiple files. As in known adaptive streaming techniques, when a user requests a particular content, the content provider transmits the requested content to the user by transmitting chunks from one or other of the encoded streams to the user. It is worth noting that the term “transmission of content” according to embodiments of the present invention, may otherwise mean “allowing content to be received”, in that the provider may either actively transmit a content to a requestor or he may place the content on a server and allow a requestor to have access to the content. As in adaptive streaming technology, the selection of the encoded stream from which a particular chunk comes may be made based on either the available transmission bandwidth at the moment that the particular requested chunk is to be transmitted or the computing capacity available to process the chunk at the receiving end for example. In other words, the selection from where a particular chunk comes from at a particular time during the delivery of the content may depend on the maximum usable bandwidth at which a transmission may be made at that time, where the maximum usable bandwidth may be dictated by the capacity of the transmission medium or the computation capacity of the requestor. As in adaptive streaming technology, the usable bandwidth may be determined a plurality of times during delivery of a requested content and so may be referred to as a current usable bandwidth. 
     In this manner, as in adaptive streaming techniques, a particular content will be received by a user as a plurality of chunks, each chunk coming from a stream encoded at a particular bit-rate. 
     Proper reconstruction of the chunks at the receiving end can be facilitated through the use of a playlist-type mechanism. Such a mechanism may be used to allow for the reconstruction of the chunks into a usable format in terms of the order of the chunks, the source of the chunks (i.e. from which stream encoded at which rate), whether the chunk is encrypted or not and, if encrypted, the source of the decryption key for example. 
     The electronic fingerprinting or watermarking technique which is permitted according to an embodiment of the present invention allows for only a subset of the complete set of chunks representing an entire content to be watermarked, rather than watermarking all of the chunks from the entire content. According to this embodiment, only a few chunks are watermarked using a unique identifying parameter associated with the requestor of the content. This has the advantage of providing sufficiently robust watermarking while minimising the amount of computer power necessary to achieve it. This process of watermarking a selected number of chunks is fast enough to ensure real-time processing and transmission to the user without the disadvantage of an added delay, apparent in the state of the art. Indeed according to a particular embodiment of the present invention, deployed in a content delivery system having an encoder for generating the streams of encoded content the chunks to be watermarked may be pre-processed by the encoder in preparation for watermarking thus allowing the subsequent watermark embedding process to be achieved in a very efficient manner by a watermarking module. According to one embodiment the watermarked chunks are encrypted and the non-watermarked chunks are not encrypted, while according to another embodiment at least some or all of the non-watermarked chunks are also encrypted. 
     The watermarking process itself can be any of the known watermarking techniques. For example according to one embodiment, watermarking involves the embedding within the content of a unique identifying parameter associated with the requestor of the content. In other embodiments of the present invention the watermarking of a chunk is achieved by encrypting the chunk whereby the encryption involves the use of a unique identifying parameter associated with the requestor of the content. 
       FIG. 1  shows a schematic of a device in which an embodiment of the present invention may be deployed. The content provider (HE) encodes a particular content (CT) into a plurality of encoded streams (ST 1 , ST 2 , ST 3 ) and stores the encoded streams, each of the encoded streams being encoded according to a different bit-rate (BR 1 , BR 2 , BR 3 ). Each encoded stream comprises a plurality of chunks (CHK 1   ST1 , CHK 2   ST1 , CHK 3   ST1 , CHK 1   ST2 , CHK 2   ST2 , CHK 3   ST2 ). According to a particular embodiment, following a request from a user for digital media content, the provider (HE) selects a plurality of chunks allowing for the content to be reconstructed, with different chunks coming from different streams according to a sequence which is predetermined by the provider. A subset of the plurality of chunks is watermarked using a unique identifying parameter associated with the requestor. The provider may also generate a playlist to keep track of the sequence and generally to keep track of information relating to the origin of the chunks, the bit-rate of the encoded stream from where the chunk came, whether or not the chunk is watermarked and whether or not the chunk is encrypted for example. This playlist may be used in allowing the user to properly reconstruct the chunks to form the content, especially in respect of the sequence or order in which the chunks are to be reassembled. When a request for content is received, the request includes a unique parameter associated with the requestor. The provider then watermarks the subset of the plurality of chunks ([CHK 1   ST1 ] WM , [CHK 2   ST1 ] WM ) using the unique identifying parameter associated with the requestor (UA). The plurality of chunks, including the watermarked chunks, is then transmitted to the requestor and the requestor reconstructs the content. According to a particular embodiment, the provider also transmits the playlist to the requestor to allow him to reconstruct the content using the appropriate chunks according to the determined sequence. If the user retransmits the reconstructed content without the authorisation of the provider and if the provider manages to intercept said retransmission, then thanks to the watermark, detectable and decodable by the provider, the user who retransmitted the content may be identified. 
     According to another embodiment the decision gas to which encoded stream a particular chunk will come from, i.e. the sequence, depends on the capability of the transmission medium at the time of transmission. In this case the provider periodically interrogates the capability of the transmission medium and selects the chunks form the appropriate encoded stream accordingly. Whenever a chunk is selected from a predetermined encoded stream (the one which is encoded using the smallest bit-rate for example), that chunk is watermarked before transmitting. The playlist is maintained in order to allow the requestor who receives the playlist to properly reconstruct the content in embodiments where such a playlist is used. 
     According to one embodiment, non-watermarked chunks are transmitted without encrypting while according to another embodiment the non-watermarked are transmitted after encrypting. 
     According to another embodiment of the present invention, the provider can predetermine which chunks will be watermarked and can cache non-watermarked chunks of content at one place on the content delivery network while the chunks to be watermarked are stored at another place on the content delivery network. When the content is requested, the latter chunks are then watermarked using the unique identifying parameter associated with the requestor. According to a variation of this embodiment, the chunks to be watermarked are pre-processed before being cached within the content delivery network. Such pre-processing may take place at the encoder for generating the streams of encoded content whereby the stream intended to be the source of watermarked chunks is already prepared by watermarking the chunks using the unique parameter associated with the requesting user as soon as such information is made available. The process of providing a watermarked set of chunks comprising a subset of watermarked chunks and a subset of non-Watermarked (remaining) chunks is thereby rendered more efficient. 
       FIG. 2  illustrates a system in which an embodiment of the present invention may be deployed. This embodiment allows for more efficient use of bandwidth consumption and load at the content provider. The system comprises a content provider (HE) and a user or requestor of content (VWR). The provider and the requestor are linked via a content delivery network (CDN) which may comprise a server (SVR) for storing content. The requestor is connected to the provider via a bidirectional communication channel (CH 1 ). The provider encodes the content (CT) into a plurality of encoded streams (ST 1 , ST 2 , ST 3 ) each at a different bit-rate (BR 1 , BR 2 , BR 3 ), each stream comprising a plurality of chunks (CHK). A subset of the plurality of streams (ST 2 ) is stored on a server (SVR) somewhere on the content delivery network (CDN) and at least one stream (ST 1 ) is stored by the provider or at another place on the network for future watermarking. The streams which are not to be watermarked may or may not be encrypted according to different embodiments of the invention. Similarly the stream which is to be watermarked may or may not be encrypted. The watermarking process itself may or may not result in the chunks of the stream being encrypted depending on different embodiments of the present invention. A user (VWR) makes a request (RQ) for a particular content (CT) via the bidirectional communication channel (CH 1 ), said request including a unique identifying parameter (UA) associated with the requestor (VWR). The requestor downloads the chunks from the stream or streams (ST 2 ) stored on the server or servers (SVR) of the content delivery network (CDN). The requestor also receives the complement of chunks necessary to reconstruct the requested content (CT), said complement of chunks being watermarked by the provider using the unique identifying parameter (UA) associated with the requestor. The choice of which chunks are to be watermarked may be predetermined by the provider before a request is received or, according to another embodiment, the choice is made at the time of transmission and is based on the capability of the content delivery network at a particular time during the transmission or on the computing capabilities of the requestors apparatus during the transmission. A playlist-type mechanism may be maintained in order to facilitate the reconstruction of the chunks from the various streams to give the requested content. 
     According to another embodiment of the present invention, also allowing for a watermark embedding or insertion process to be achieved in a very efficient manner, the pre-processing step includes the provider watermarking chunks from a chosen stream in advance of any request from a user. In this case the provider generates a plurality of unique keys and uses one of these unique keys to generate watermarked chunks in readiness to be used to generate a watermarked content. In this manner the provider prepares a plurality of sets of watermarked chunks using the plurality of unique keys such that each set of watermarked chunks is ready to be used to generate uniquely identifiable watermarked contents intended for users who subsequently requests the content. Furthermore, since a request from a user includes a unique identifying parameter associated with that user, this allows the provider to maintain a database associating each unique key with each unique identifying parameter associated with each of the users to whom the corresponding watermarked content was delivered, thus rendering the watermarked contents traceable. 
     In an embodiment where the selection of chunks to be modified is bated on the usable bandwidth, it could ensue that the resulting so-called watermarked content does not actually contain any watermarked chunks. This could happen for example if the usable bandwidth were always high enough to allow for streams encoded at the highest bit-rate to be delivered. In this case it is sufficient for the content delivery system to include a mechanism which makes sure that at least one watermarked chunk is included in a watermarked content. It is worth noting that in such a case of forced watermarking, as is the case with any of the embodiments of the present invention, chunks from any of the streams may be chosen as being chunks to be watermarked and not necessarily only chunks from the lowest bit-rate encoded stream. 
     As mentioned previously, according to embodiments of the present invention, a pre-processing step may be carried out when generating the plurality of encoded streams in order to have watermarked chunks already prepared for a subsequent watermark embedding or insertion process. 
     According to one embodiment of the present invention the watermarked chunks require a separate key for decryption and the requester needs to be properly authenticated before the chunks are delivered. The authentication information could indeed be used to embed unique information in the watermark/fingerprint. 
     According to another embodiment, the content delivery network comprises an insertion server which handles the insertion of the watermarked chunks into the delivery of a requested content. This allows the simplification of the gathering of information during a process for detecting watermarks whenever required. Such an insertion server would need to respond to many requests however since only a few chunks of a particular content requires to be watermarked, according to the invention, then the load would be distributed better than in state of the art watermarking solutions wherein the whole content is watermarked. The number of chunks to be watermarked and their location within the content may be optimised for best performance while maintaining adequate security. 
     The method proposed by the present invention allows for the content to be identified using existing mechanisms for retrieving a signature of a content. Specific chunks can be identified within the content and the fingerprint/watermark retrieved in a very efficient way thanks to the invention. 
     According to embodiments of the present invention, when a user receives a requested content he receives all of the chunks required to be able to reconstruct and view the entire requested content. The provider does not defer the transmission of chunks that have been pre-determined as requiring watermarking pending a further request from the user for any such missing chunks. Indeed, the content which is transmitted following a request is sufficient to allow an authorised user to view the content with no degradation as would be the case had some chunks been withheld from the transmission. All non-watermarked and watermarked chunks are transmitted following a request for the content.