WO2005018234A1 - Procede et systeme de fourniture de donnees de media - Google Patents

Procede et systeme de fourniture de donnees de media Download PDF

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Publication number
WO2005018234A1
WO2005018234A1 PCT/US2003/021947 US0321947W WO2005018234A1 WO 2005018234 A1 WO2005018234 A1 WO 2005018234A1 US 0321947 W US0321947 W US 0321947W WO 2005018234 A1 WO2005018234 A1 WO 2005018234A1
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WIPO (PCT)
Prior art keywords
subset
data
representation
service
quality
Prior art date
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PCT/US2003/021947
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English (en)
Inventor
Antonio Ortega
Scott M. Darden
Asha Vellaikal
Zhourong Miao
Joseph Caldarola
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Citipati Partners, Llc
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Publication date
Application filed by Citipati Partners, Llc filed Critical Citipati Partners, Llc
Priority to PCT/US2003/021947 priority Critical patent/WO2005018234A1/fr
Priority to AU2003251896A priority patent/AU2003251896A1/en
Priority to EP03818145A priority patent/EP1661401A4/fr
Publication of WO2005018234A1 publication Critical patent/WO2005018234A1/fr

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Definitions

  • the present invention is concerned with techniques for transmitting and delivering media data in a communications network.
  • Communications networks e.g. the Internet
  • Such data is in digital form, and may represent a still image, a video sequence, or an audio sequence of voice or music, for example.
  • Rendering of time-based digital media such as audio, speech or video involves producing a series of outputs over a period of time, e.g., a video frame every 1/30-th of a second in the case of video NTSC output.
  • security measures are required for preventing contents from becoming available at intermediate points and for restricting access to the data to those who have been properly authorized.
  • Such measures may include encryption as well as partitioning of data for transmission of the individual parts over distinct paths.
  • parts are chosen so that no one of them provides a good approximation to the original content, thus requiring complete assembly of all parts for content to become available at good quality to an authorized recipient.
  • Similar concerns arise with respect to security and privacy in communications over an open network, especially in real-time communication between users and in real-time broadcasting of potentially sensitive information.
  • Data representing media content tends to be voluminous, and its protection typically entails considerable complexity and transmission costs: in encryption, in transmission over a secure server, and in the use of streaming in preference to downloading to make copying more difficult.
  • Summary of the Invention Techniques of the invention can provide for protection of media data at reduced cost in that protective measures may be applied to one or several data subsets having a comparatively small size. The subset(s) can be selected such that protection of the complementary bulk of the data becomes less important.
  • time-based formats are MP3 audio and MPEG2 audio and video.
  • a data set/sequence representing the title is partitioned into smaller subsets/subsequences, each having a specific access control mechanism, e.g., download-only, streaming-only or download-or-stream, and each being associated with reconstruction logic information for reassembly of the original title.
  • a first of the subsets is chosen relatively large, yet to convey a degraded-quality representation of the title, and the others for complementing the first subset to obtain a superior-quality representation.
  • Fig. 1 is a schematic of operation of an authoring module.
  • Fig. 2 is a schematic of different partitioning of a media sequence.
  • Fig. 3 is a schematic of a relationship between authoring module, metadata server and content distribution system.
  • Fig. 4 is a schematic of interaction between a client and a content distribution cloud.
  • Fig. 5 is a schematic of operation of a media distribution service.
  • Fig. 6 is a schematic of processing at a client.
  • Fig. 7 is a schematic of an encoder for data compression.
  • content may be delivered in different forms, to different types of terminals.
  • one terminal may be a closed system, e.g. a TV set-top box, and another an open system such as a PC.
  • the distribution mechanism need not be uniform, as it may include means such as direct satellite broadcasting, Internet streaming, or distribution of content in a recorded physical medium such as a disk, for example.
  • a content owner or service provider will seek to secure the content in all cases and regardless of differences in delivery formats and means.
  • There are three aspects of delivery systems which are considered as particularly important.
  • decoder means should be inexpensive, as with set-top boxes or other hardware to be bought by the end user, and decoding should be fast, e.g.
  • the third aspect is with content protection desirably offering easy preview of content.
  • O(LAN) For encryption of N bits of data, the over-all complexity is O(LAN) which can be substantial.
  • O(LAN) For example, in the RSA cryptographic algorithm (named after its originators Rivest, Shamir and Adleman), encryption and decryption involve exponentiation by a large integer followed by a modulo operation.
  • input data is processed to extract content-dependent key information whose length in bits here is denoted by L'.
  • a compression system involves one encoder and at least one decoder.
  • the encoder generates a compressed representation of the signal that can be read by the decoder to produce an approximation to the input signal.
  • Open international standards developed to date including such broadly used standards as MPEG-2 or JPEG, specify the syntax of the bit stream exchanged by encoder and decoder. Their goal is to maintain inter-operability between encoders and decoders of different vendors.
  • the standards prescribe how the decoder should interpret a bit stream, and the operations to be performed on the data to reconstruct the signal.
  • the standards documents do not specify how the encoding process needs to be performed, only how the encoder can represent the information to be sent to the decoder.
  • many different encoding strategies can be employed while still preserving syntax compatibility with a standard decoder, e.g. as based on the MPEG-2 standard, in the sense of the decoder being able to decode the information.
  • a cryptographic algorithm customarily is applied directly to the compressed stream, which then is no longer syntax-compatible.
  • a preview of the media stream requires a separate, low-resolution file.
  • Known techniques for providing the latter result in inefficiency, e.g., when a so-called scalable video coding is used, particularly when the preview is distributed first and the rest of the signal is provided only to those end users that have been granted access. In this case, the preview containing a small portion of the data is pre-positioned, i.e., available to the end user, and a large amount of additional data has to be transmitted to view the signal at the higher resolution.
  • the additional data has the most value, and its encryption and decryption will be costly.
  • two data sets are derived from an original compressed video, namely a base layer with rate Rb and an enhancement layer with rate Re, where Rb « Re.
  • the enhancement layer has to be fully encrypted, or else a selective encryption would have to be performed to guard against decoding of the enhancement.
  • a low-resolution preview file in fact contains most of the data, typically by a wide margin, so that Rb » Re using the above notation.
  • the low-resolution file contains at least 80% or even 95% of the total data.
  • information can be removed at different stages of encoding, desirably while preserving syntax compatibility.
  • Privacy/Security in Network Communications Characteristics of a reverse-scalable system are advantageous also for security and privacy in communications over an open network such as the Internet, especially in real-time applications such as VoIP (Voice over Internet Protocol), video conferencing, and real-time broadcasting where potentially sensitive information may be transmitted.
  • VoIP Voice over Internet Protocol
  • video conferencing video conferencing
  • real-time broadcasting where potentially sensitive information may be transmitted.
  • a coiporation will have reservations against use of an open network for conducting remote business meetings.
  • VPN virtual private network
  • content can be separated into subsequences at the source, or at network gateways.
  • a relatively small subsequence can be formed to convey key information, while a much larger subsequence provides a low-quality approximation to the signal which by itself may be essentially useless.
  • Fig. 1 shows an authoring module 10 accepting media sequence input and additional parameter input, and generating N subsequences along with respective reconstruction logic.
  • the authoring module 10 serves for analyzing/splitting the input sequence into the subsequences, and it generates the reconstruction logic for recombining some or all of the subsequences after their delivery.
  • the reconstruction logic may be bundled together with the subsequences, or, in a different implementation, they can be made available independently.
  • the subsequences can be delivered in various ways, such as downloading or streaming, for example. In downloading, a data file is delivered in its entirety prior to its use, e.g. by direct server-to-client transfer, by transfer to the client from a third processor acting as caching proxy, or by a transfer from another user in possession of the file as in a so-called peer-to-peer network.
  • variants (a), (b) and (c) for analyzing/splitting a time-based media sequence into subsequences 1 and 2.
  • the sequence is to be split into two subsequences.
  • splitting is by a switch 21 for allocating bits to one or the other of the subsequences based on a chosen splitting scheme which does not rely on knowledge of any coding format adhered to in the sequence 20.
  • the analyzer utilizes certain l ⁇ iown coding information. Such information may enable splitting such that at least one of the subsequences may be playable to some extent, albeit abbreviated or at a lower quality, for example.
  • codec parser 22 the media sequence is first parsed based on the information, and the parsed sequence is then split by a switch 23.
  • Variant (c) provides for splitting by analyzer 24 without any further partitioning prior to delivery. In each of the cases, the original sequence and/or any of the subsequences may be enciypted, then requiring corresponding decryption after delivery.
  • Fig. 3 shows authoring module 31 generating media subsequences being delivered to a content distribution system 32 serving three destinations where content may be displayed or archived, for example. The authoring module 31 further generates metadata which are forwarded to a metadata server 33. Metadata provide information which is ancillary to the actual subsequence bit streams, e.g.
  • subsequence file identification unique naming is straightforward in a centrally controlled system, by following a chosen format assigned to a media title.
  • a name server can act as a mechanism for preventing subsequence identifier conflicts.
  • the authoring module then can query the name server for unique identifiers for each new media title to be introduced into the distributive system.
  • different sequences may be specified for downloading or streaming, for example, and for downloading there may be a specification of priority of one subsequence over another.
  • Fig. 4 illustrates a specific instantiation of interaction in a media distribution service, between a client 41 and a content distribution facility or Aclouds 42.
  • Such a service can utilize existing media distribution systems and infrastructures, e.g. the Internet.
  • certain supporting systems are provided.
  • a client is considered who requests audio playback of a media title A.
  • Aplay the client receives a reply from the media distribution service including instructions for deciphering the subsequence access information and for reconstruction of the title from the subsequences.
  • the reply designated as Media Title Locator (MTL)
  • MTL Media Title Locator
  • MSRL Media Subsequence Resource Locator
  • the MSRL of a subsequence includes media server information, access protocol information, and the subsequence file name. In case the reconstruction logic is not bundled with the subsequence, the MSRL also includes information for accessing the corresponding logic.
  • FIG. 5 more specifically illustrates operation of a media distribution , service.
  • a client computer 51 submits its request for a media title to the media distribution response server 52.
  • the response server 52 queries the metadata server 53 to retrieve one or several required subsequences, logic and any other relevant information.
  • the response server 52 queries the directory service 54 for the locations of the individual subsequences/logic, with the directory service 54 possibly having intelligence for choosing optimal locations in a case where a subsequence can be obtained from different locations.
  • the response server 52 combines the information to form the MTL and sends it to the client 51.
  • the client 51 parses the MTL and opens connection with the individual media servers 55 to obtain the subsequences/logic.
  • File distribution can involve an available mechanism, e.g. client-server distribution, edge-of-network/push caching, pull caching as in standard passive caching and peer-to-peer file sharing. Such mechanisms may be categorized as being of one of two types, media server versus directory service.
  • the role of a media server, central or distributed, includes storing the subsequences and serving or streaming them on demand to any requesting client.
  • a central server can be used in a service where a user can download or stream directly from a main service provider in a client-server mode.
  • a file sharing service replicates a file at multiple locations at Aedges ⁇ , such as mirrors and proxies of the network, but in a more controlled fashion as compared with peer-to-peer.
  • a further example for a server includes cache proxies in the network for storing recently requested information.
  • Subsequences can be made available as downloaded or streamed, and, in streaming, multicasting can be provided for multiple users to listen to the same song, for example.
  • subsequences When subsequences are not encrypted or otherwise constrained, they can be copied to disk, transferred, removed, backed up, and the like.
  • a directory service a listing/record is maintained of the locations of the individual subsequences, for supporting a querying interface.
  • the directory service can be a simple database on a single server.
  • a decentralized service e.g. peer-to-peer, multiple users can each have a copy of the same file, with availability varying as a function of who is logged on.
  • a media distribution system as illustrated above can be implemented for a variety of uses including an online media locker, online jukebox, chat room, or advertising means, for example.
  • an online media locker users can store digital media content they already own, e.g. from a CD, enabling the user to access the content from any computer connected to the network. If allowed by the content provider, storing may be of the fully reconstructed file, or of a lower-quality version. Also, an original file may be split into one portion which can be downloaded, and another to be obtained by streaming from a server whenever playback is desired.
  • subscribers have access to music in a database.
  • Users may obtain portions of music for downloading, of a quality which is inadequate for satisfactory playback and requiring a complementary portion which may be obtained by relatively low-rate streaming.
  • streams can be multicast such that the streams trigger playback. From users, comments may be overlayed on the music.
  • Other media e.g. images or video can be distributed correspondingly, with partitioning of original data based on the technique of the invention.
  • application of the technique is not limited to visual and auditory media, but can extend to tactile media, for example.
  • Compression as exemplified below is used in numerous media applications such as speech, audio and video, including DVDs, broadcasting by cable or satellite, and streaming video over the Internet.
  • a media sequence can be partitioned in the course of compression-encoding prior to transmission, under standards such as MP3, MPEG-2 or MPEG 4, into subsequences which can be decoded by a conesponding standard decoder.
  • a media sequence that is already in compressed format can be read and parsed for partitioning.
  • the partitioning can be effected during compression, or later on the compressed stream.
  • recombination can be effected in the course of decoding or before.
  • Fig. 7 shows a basic structure for a compression system, including a motion estimation module 71, a motion compensation module 72, a transform and quantization module 73, a reconstructed-frame memory 74, a DC differential pulse code modulator (DPCM) 75, an AC zig-zag run length module 76, and variable-length coders 77 and 78.
  • Functionality of modules involves the following: DCT Transform. From input blocks of pixels, typically blocks of size 8 by 8, the same number of samples of the frequency contents of each block are generated, typically called frequency coefficients.
  • This transform is invertible, so that, if no further processing is performed, the original pixel values can be recovered by applying an appropriate inverse transform.
  • the output coefficients represent the information content of each input signal in the frequency domain.
  • the transforms provides significant energy compaction, i.e., for typical images the number of frequency coefficients needed to provide a good representation of the signal tends to be small. While DCT (Discrete Cosine Transform) is prevalent in current data compression techniques, use of other transforms, e.g. wavelet transforms, is not precluded. Wavelet transforms are used in the JPEG 2000 standard and are likely to find use in video coders. Quantization.
  • the frequency coefficients which can take any real values within an interval that is known beforehand, are quantized to the closest among a discrete set of values. Thus, the quantized coefficients take only a discrete set of values. This operation is lossy, amounting to a many-to-one mapping, and cannot be inverted. Entropy Coding. Also l ⁇ iown as variable-length coding, the quantized values are represented by specific variable-length codes designed such that the most likely quantized values are assigned shorter code lengths. This process is lossless, i.e., the mapping from quantized value to code is one-to-one, and once the coded symbols have been concatenated for transmission there is a unique way of parsing the bit stream to obtain the individual codes. Motion Estimation and Compensation.
  • Motion estimation is only performed at the encoder, while motion compensation is performed at both encoder and decoder.
  • Motion estimation consists of dividing a current frame into blocks, typically 16 by 16 pixels in size, and for each block finding the block in a specified region in the previous frame that most closely matches it. If the match is sufficiently good then a motion vector is transmitted and the difference between the block in the current frame and the best-match block from the previous frame will be compressed and transmitted. Otherwise, if the match is not sufficiently good, the block in the current frame will be compressed directly, without subtraction of any information from the previous frame.
  • the encoder can be modified for removing information in the course of encoding. Then, after such partial removal of information, the output from the encoder can be taken as a first subsequence, with the removed portion as a complementary subsequence.
  • an analyzer filter can be formed for combining partial decoding of a compressed file with removal of information for partitioning. For removal of information it is desired to adhere to syntax-compatible strategies in the sense described above, for at least one of the subsequences, typically the one containing the bulk data. The following are examples of such strategies: AC Coefficients.
  • the AC coefficients are coded with a variable length code (VLC) where two dimensions are encoded, run-length and magnitude. Escape codes are used for all values outside the table of codes.
  • VLC variable length code
  • Escape codes are used for all values outside the table of codes.
  • selected AC coefficients are set to a specified value, e.g. zero, with the actual value placed in a supplementary stream. Because of the run lengths, if any coefficient is changed to zero, as the run of zeros now has become longer, this alters not only its code but also the code before it. Therefore, some form of re-encoding of the block may be needed. Zeroing the AC coefficients distorts the image texture, leaving an unappealing, though recognizable sequence. Another option is to set the sign of certain AC coefficients to be positive.
  • a third option is to remove the coefficient and replace it with a number indicating the distance to the next bits that will be changed.
  • a fourth option is to remove the coefficient without replacement, resulting in a shift, by one, of all the following coefficients in the zig-zag scan.
  • the AC coefficients are appealing for encoding a distance because their range is from -2048 to 2048 (but not zero). This is long enough in most cases, and, if need be, two coefficients can be used to code the jump, making for 24-bit distance.
  • Replacing coefficients has the advantage of a recombination filter of low complexity, as recombination can skip bits without parsing them, but provides less control over the quality of a resulting first subsequence.
  • Removing coefficients without replacement has complexity similar to zeroing, with a potential advantage in introducing significant quality degradation even if just a single coefficient is removed.
  • the following are among options: (i) the N largest coefficients of a block, (ii) the first N coefficients of a block, and (iii) the coefficients that provide the maximum average energy over a subset of the sequence, e.g. a frame or a group of pictures (GOP).
  • a further possibility lies in selection of blocks for coefficient removal, e.g.
  • DC coefficients are differentially coded, with a new sequence starting at the begimiing of each line of 8 by 8 blocks. The first value of a new line is between 0 and 255. The difference values range form -255 to 255. All coefficients are variable-length coded. Altering the DC vectors impairs the fidelity of the video and has a number of options. Zeroing the vectors produces marginally acceptable video in which some of the video contents can be made out.
  • altering the signs of the DC differentials is another choice. Because the range of differential vectors is from -255 to 255, if all signs are set in one direction, e.g. all positive, or even if a single sign is changed on a chosen line, the predicted DC value of a block can be outside the 0-255 range. Thus, an attacker might be able to determine that a particular sign should be changed when out-of-range coefficients are observed. Many practical media players simply truncate the DC values if they fall out of range.
  • a further option involves eliminating the MV temporal direction information for each block of a B-frame.
  • a code table can be used to represent each of the possible values of this information, along with other parameters.
  • the code that is used is not unique but depends on the values taken by the other parameters encoded.
  • one multi- bit code has to be replaced by another where the temporal direction has been modified.
  • Other options that are applicable to most of the above include coding only P-frames or only one of the MV directions. Combination of Techniques. It is feasible to change multiple elements of the bit stream. Not only will this reduce the quality, but may also make unauthorized decoding more difficult, thus enhancing security. Also, certain techniques as described above can be combined with known scrambling techniques.
  • the supplemental stream then contains only the coefficients packed together, and the filter can run through the file quickly, swapping and skipping.
  • a seek-and-swap method one concern arises from the fact that the number of bits allowable for skipping actually depends on what the MPEG format permits for a specific coefficient.
  • the DC coefficients are used then there is a range of 256 values for unpredicted blocks, and of 512 for predicted blocks. Therefore, skipping is constrained to 256 or 512 bits. While most block sizes are considerably less than 256 bits, larger blocks may have to be accommodated. AC coefficients may present a better choice, as they provide 4096 bits of precision.
  • a technique of the invention can provide for removal of either DC or AC information, selectively depending on the degree of image degradation desired for a scene in a video sequence. Such dependence can be selected to advantage for providing a file with a preview functionality, for example. When informed as to which scenes have been degraded lightly, a user can view these scenes as a preview of the complete sequence.
  • Optimization of Data Removal As described, the level of protection offered by our techniques depends on the number of values that can result in a valid bit stream in the position where data has been removed. For example, when a differentially encoded DC coefficient is removed, there are exactly 512 different values possible in that position. To reconstruct the original compressed signal, a hacker would have to guess which among the 512 possible values is the right one.
  • the DC sign when the DC sign is set to Aalways positives, Ri equals one bit per DC coefficient, Di depends on both the change in the coefficient itself and on the subsequent DC coefficients which will be affected in differential coding, and Ni equals 2.
  • the goal can be the maximizing of a weighted cost function, namely Di + k ⁇ Ni, where k is a Lagrange multiplier allowing emphasis on distortion or level of protection in optimization.
  • the number of "good" options can be approximated by the entropy of the random variable representing them. For example, when a sign is removed, the two options typically have the same likelihood.
  • the level of protection achieved is directly related to the number of bits required to represent the information that was removed, and an approximate formulation for optimization calls for maximizing Di + k ⁇ Ri, where a large value is desirable for Ri in that it represents a large number of options to be chosen in order to restore the data.
  • Techniques of the invention can be implemented in software, for a processor to follow program instructions stored in memory. It was with such an implementation that experimental results were obtained as presented below. For commercial use, in the interest of enhanced efficiency, use of firmware and/or dedicated hardware is indicated, e.g. at a network gateway. Whether by hardware, firmware or software, the techniques can be implemented as separate modules, or their functions can be integrated in encoder and decoder modules.
  • the size of the bulk file remains close to the size of the original file, and the supplemental streams are small by comparison. Even the supplemental file including the most information, namely the one conveying selected AC coefficients, remains less in size than 10% of the original file.
  • respective supplemental files of approximately 1% and 0.2% in size are noted. Techniques including removal of the DC coefficients or their sign result in highly degraded video sequences. Upon removal of the AC coefficients or their sign there results a moderate decrease in quality.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Computer Security & Cryptography (AREA)
  • Databases & Information Systems (AREA)
  • Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)

Abstract

Dans la communication de média, par exemple dans la fourniture de données vidéo et audio ou dans la téléconférence, un fichier ou titre de média divisé en vue d'une livraison sure et efficace. Un séquence de données représentant le fichier est divisée en sous-séquences plus petites, une première sous-séquence étant choisie pour acheminer une représentation à qualité dégradée des données et les autres séquences étant choisies pour compléter la première sous-séquence de manière à obtenir une représentation de qualité supérieure. Les domaines d'application dudit procédé sont les média à la demande, les communications et la diffusion en temps réel et les services en ligne de distribution de média par casier (locker), de jukebox et de messagerie en temps réel.
PCT/US2003/021947 2003-07-15 2003-07-15 Procede et systeme de fourniture de donnees de media WO2005018234A1 (fr)

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EP03818145A EP1661401A4 (fr) 2003-07-15 2003-07-15 Procede et systeme de fourniture de donnees de media

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