Abstract:
A system and method for streaming data over a communications network with varying streaming conditions, includes conditioning a data stream to create conditioned data representations including encoded representations targeting running conditions, wherein conditioning includes partitioning the data stream into data units, and generating the encoded representations of each of the data units, packaging the conditioned data representations with metadata specifying a target set of running conditions, wherein the conditioned data representations are packaged by pre-computing one or more trajectories among the encoded representations based on a given finite set of streaming conditions, observing a current run-time condition and selecting one of the packaged conditioned data representations for streaming over the computing network according to the running conditions in view of the current run-time condition in accordance with the observed current streaming condition, and a communications network responsive to the media server for streaming the selected packaged conditioned data representation.

Description:
BACKGROUND 
   Media compression and delivery provide an indispensable modality for multimedia communications. Various applications exist, including digital TV, video on demand, video e-mail, videophone, video conferencing, and rich media e-learning. These applications have been exemplified most prominently by the IP-based World Wide Web and wireless communications services. Faster development and wider deployment of rich media communications is foreseen for the near future, as higher access bandwidth through cable and digital subscriber loop modems become available, server and network load is reduced through large-scale deployment of IP multicast, and the backbone bandwidth increases. 
   Unfortunately, unlike more traditional networks such as ISDN, which may provide a guaranteed quality of service (“QoS”) for connections, both the IP-based Internet and wireless networks are relatively unreliable. Currently, they offer no QoS guarantees. QoS-guaranteed transmission for all rich media streams in their entirety is infeasible and may remain so for a long time owing to technical and economical constraints. Unavoidable packet loss, bit error, burst error, delay, and jitter make the effective transmission of rich media over such lossy networks a challenging task. These network characteristics influence the transmission of compressed bit streams, alter the nature of the end-to-end quality, and essentially call for renewed design of the rich media delivery system. 
   Thus, it is desirable that a media server be able to adapt the content to the current conditions. Adaptive media services are the focus of the present disclosure. For example, if a client requests the progressive delivery of a video sequence over a lossy wireless channel, the media server should adapt the streamed content to both varying packet loss ratios and available channel rates. This adaptation would yield a better user experience. It is especially desirable that such an adaptation should not require tremendous processing power at the media server, which is the case for typical online transcoding techniques. 
   SUMMARY 
   According to an embodiment of the present disclosure, a method of streaming data over a communications network with varying streaming conditions, said method comprising conditioning a data steam to generate a plurality of conditional data representations of the data stream, wherein the conditioned data representations comprise different encoded representations of source data of the data stream each targeting a different set of running conditions, wherein conditioning comprises partitioning the data stream into a plurality of data units, and generating the different encoded representations of each of the data units of the data stream, packaging the plurality of conditioned data representations of the data stream together with metadata that specifies a target set of running conditions associated with the different encoded representations of the data stream, wherein the conditioned data representations are packaged by pre-computing one or more trajectories among the plurality of different encoded representations for each of the data units based on a given finite set of streaming conditions, observing a current run-time condition of a computing network, and dynamically selecting one of the packaged conditioned data representations for streaming over the computing network according to the running conditions specified in the metadata of the packaged conditioned data representations in view of the current run-time condition of the computing network. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present disclosure teaches a system and method for Multiple Description Hinting and Switching for Adaptive Media Services in accordance with the following exemplary figures, in which: 
       FIG. 1  shows a schematic block diagram for a system according to a preferred embodiment of the present disclosure; 
       FIG. 2  shows a flow diagram for packaging in accordance with  FIG. 1 ; 
       FIG. 3  shows a flow diagram for streaming, given metadata from packaging, in accordance with  FIG. 1 ; 
       FIG. 4  shows a schematic set of sequential descriptions, where each description is a compressed access unit that is ready to be delivered by a server and, for example, the descriptions from i−2 to i+4 could represent the compressed video frames of a video clip; 
       FIG. 5  shows a schematic set of sequential descriptions with one description per access unit, where a media server sends these descriptions sequentially whatever the observed and/or computed running conditions xc are, which may result in perceptual degradation with amplitude proportional to |x−xc|; 
       FIG. 6  shows a schematic set of discrete target running conditions xc i , such as for Sure-Streaming from Real Networks; 
       FIG. 7  shows a schematic set of sequential descriptions, where description i is described by its properties p, and where the listed properties (i.e. type, size, distortion, robustness) are merely exemplary; 
       FIG. 8  shows a schematic set of sequential descriptions with metadata attached to every description, this metadata describing the description&#39;s properties; 
       FIG. 9  shows a schematic set of sequential descriptions where a media server analyzes the metadata of all the descriptions pertaining to the access unit under consideration, and decides which description to send depending on the observed and/or calculated running conditions; and 
       FIG. 10  shows a schematic set of sequential descriptions where D i   k (.) denotes MSE(D i   k )(:), and considering the access unit i+1, N i =3 values are computed at description 2 denoted by alpha i+1   2 (k) for k in [0, N i,  and these N i  values are stored and the description j kept such that j=arg max k  D i+1   2 (k), with the maximum distortion at time i+1 and description 2 denoted by D i+1   2 . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   A system and method for Multiple Description Hinting and Switching for Adaptive Media Services are provided. In the description that follows, the following terms are pre-defined: 
   Access Unit: An access unit is a media unit to which embodiments of the present disclosure apply, such as, for example, video pictures in a video sequence or audio frames in a sound track. 
   Description: A description is a compressed access unit that is ready to be delivered by a server. 
   Description Properties: A vector of properties relative to a particular description, the vector denoted by “p”. This vector describes a particular description in a way that is compliant with a specific implementation or embodiment of the present disclosure. 
   Running Conditions: A vector of actual conditions to which a server must adapt, the vector denoted by “xc”. 
   Embodiments of the present disclosure attach a piece of information or “metadata” to every single description. This metadata characterizes a description in terms of the description&#39;s properties in a way that is compatible with the implementation of a Description Selection algorithm. A media server analyzes the metadata of all the descriptions pertaining to the access unit under consideration, and decides which description(s) to send depending on the observed and/or calculated running conditions xc. That is, there are no predefined trajectories among the different descriptions. Instead, the media server picks at every time instant or access unit duration the most appropriate description(s) with property p such that |x(p)−xc| is minimum under pre-established constraints. 
   As shown in  FIG. 1 , a system embodiment of the present disclosure is indicated generally by the reference numeral  101 . The system  101  includes a Conditioning tool  100  for receiving data, a Packaging tool  200  in signal communication with the Conditioning tool  100 , and a media server  300  in signal communication with the Packaging tool  200  and an Internet  400 . The Conditioning tool  100  takes source data in and splits the source data into a series of data units (e.g., a video stream may be split into a series of video frames). The Conditioning tool then creates multiple versions of each data unit, with possibly a variable number of versions per data unit, given a set of expected running conditions. 
   Turning to  FIG. 2 , a flow diagram for packaging in accordance with  FIG. 1  is indicated generally by the reference numeral  201 . An initialiaztion block  210  passes control to a counter block  212 , which, in turn, passes control to a decision block  214 . The decision block  214  checks whether the counter has reached the number of access units, and if so, passes control to an end block  216 . If the counter has not reached the number of access units, it passes control to a loop initialization block  218 , which, in turn, passes control to a function block  220 . The function block  220  retrieves metadata of a description according to a local loop counter at a time corresponding that tracked by the counter block  212 , and computes a maximum distortion. An internal loop counter block  222  receives control from the block  220 , increments the local loop counter, and passes  control to a decision block  224 . The decision block  224  checks whether the local loop counter is less than a limit, and if so, passes control back to the function block  220 . 
   Control is passed to a loop initialization block  226  if the block  224  determines that the local loop counter has reached the limit. The loop initialization block  226 , in turn, passes control to a function block  228  that retrieves two descriptions, checks whether a previously computed distortion is less than the distortion between the two retrieved descriptions, and computes a value alpha. The function block  228  passes control to a counter block  230 , which increments an inner loop counter, and, in turn, passes control to a decision block  232 . The decision block  232  checks whether the inner loop counter is less than a limit, and if so, passes control back to the function block  228 . If the decision block  232  finds that the inner loop counter has reached the limit, control is passed to an outer counter block  234 , which, in turn, passes control to a decision block  236 . The block  236  checks whether the outer loop counter is less than a limit, and if so, it passes control back to the function block  228 . If the decision block  236  determines that the outer loop counter has reached the limit, it passes control to a write block  238 . The write block  238 , in turn, writes the metadata alpha and passes control back to the counter block  212 . 
   Thus, the Packaging tool  200  packages the various versions into a file, such as on disk, and attaches metadata such that a streaming server can effortlessly determine the most appropriate trajectory among these versions to target current observed running conditions (i.e., xc in  FIG. 1 ). 
   Turning now to  FIG. 3 , a flow diagram for streaming, given metadata from packaging in accordance with  FIG. 1 , is indicated generally by the reference numeral  301 . Here, an initialization block  310  passes control to a counter block  312 , which, in turn, passes control to a decision block  314 . The decision block  314  checks whether the counter is less than the number of access units, and if not, passes control to and end block  316 . If the counter is still less than the number of access units, control is passes to a function block  318  to compute a running constraint R. The function block  318  passes control to a retrieval block  320  to retrieve the current limit Ni, and, in turn, pass control to a function block  322 . The function block  322  retrieves the current alpha and computes Ni distortion values for the description. A function block  324  receives control from the function block  322 , selects a description corresponding to the current counter time value for streaming, and passes control back to the counter block  312 . 
   Thus, a Streaming Server  300  periodically measures the current running conditions xc from the System  400  over which the packaged data may flow. A customer comes in and requests the data previously conditioned and packaged. The Streaming Server thereby reads data from the packaged data, retrieves the various versions at time t along with the attached metadata, and computes the most appropriate subset of versions to send at time t given xc for all times t between time 0 and time T (i.e., the end of the packaged data). 
   As shown in  FIG. 4 , a schematic set of sequential descriptions is indicated generally by the reference numeral  401 . Here, for example, the descriptions from i−2 to i+4 could represent the compressed video frames of a video clip. Every access unit has one and only one description to create a typical single encoding of a media stream. For example, if an uncompressed video clip is composed of 100 frames or access units, compressing this video clip results in each video frame being compressed once, thereby resulting in 100 descriptions for a one-to-one mapping. A file containing these 100 descriptions is then loaded on a media server. 
   Turning to  FIG. 5 , a schematic set of sequential descriptions with one description per access unit is indicated generally by the reference numeral  501 . A media server sends these descriptions sequentially whatever the observed and/or computed running conditions xc are, which may result in perceptual degradation with amplitude proportional to |x−xc|. 
   The media server sends the descriptions when playback is requested. Since a description results from digitally compressing an access unit, the compression parameters (e.g., CODEC, bit rate) directly affect the descriptions&#39; properties (e.g., size, distortion). Thus a sequential set of descriptions optimally targets one and only one set of running conditions xc. We denote by x the running conditions a set of sequential descriptions targets. 
   Turning out of sequence to  FIG. 7 , a schematic set of sequential descriptions, where description i is described by its properties p, is indicated generally by the reference numeral  701 . Here, the listed properties (e.g., type, size, distortion, robustness) are merely exemplary. The x strongly depends on the encoding properties p. Presentation quality is degraded when a media server sends descriptions targeting x under actual running conditions xc whenever x is different than xc. Due to the best effort nature of IP networks, x different than xc is a common scenario. Others have identified this problem and have brought different solutions. 
   A first solution was to capture every unique description before it was actually sent over the network and to perform some processing on it (e.g., a transcoding algorithm). While this solution provided a fine-grained scalability property (one could make |x−xc| as small as possible), it also resulted in tremendous processing requirements, and thereby dramatically reduced the number of concurrent streams the media server was capable of handling. Another solution created multiple descriptions per access unit. The present disclosure builds on this paradigm. 
   Turning now to  FIG. 6 , a schematic set of discrete target running conditions xc i , such as for Sure-Streaming from Real Networks, is indicated generally by the reference numeral  601 . Existing implementations rely on a discrete set of target running conditions x i  (e.g., Sure-Streaming from Real Networks).  FIG. 6  graphically depicts the idea. Multiple descriptions per access unit (four in the Figure) are created such that four distinct sets of descriptions exactly target running conditions x 1 , x 2 , x 3  and x 4 . The media server observes and/or calculates the running conditions xc and may decide to switch to a different distinct set of descriptions x i  (i={0, 1, 2, 3} in the Figure). This solution requires a negligible amount of extra processing power, but the level of granularity for adaptation has a direct impact on storage space. 
   Embodiments of the present disclosure combine advantages of both worlds. That is, the embodiments provide a generic framework by which fine-grained scalability may be achieved at a negligible impact on the required processing power. 
   As shown in  FIGS. 8 through 10 , to be described together, operation of a preferred embodiment is described where a set of descriptions D is given for a particular video asset. Delta denotes the constant inter-frame interval. For example, a video sequence at 25 frames-per-second has a Delta of 1/25 s. 
   As shown in  FIG. 8 , a schematic set of sequential descriptions is indicated generally by the reference numeral  801 . Metadata is attached to every description for describing the description&#39;s properties. 
   As shown in  FIG. 9 , a schematic set of sequential descriptions is indicated generally by the reference numeral  901 , where a media server analyzes the metadata of all the descriptions pertaining to the access unit under consideration, and decides which description to send depending on the observed and/or calculated running conditions. 
   As shown in  FIG. 10  a schematic set of sequential descriptions is indicated generally by the reference numeral  1001 , where D i   k (.) denotes MSE(D i   k )(:), and considering the access unit i+1, N i =3 values are computed at description 2 denoted by alpha i+1   2 (k) for k in [0, N i , and these N i  values are stored and the description j kept such that j=arg max k  D i+1   2 (k), with the maximum distortion at time i+1 and description 2 denoted by D i+1   2 . 
   Let D i   j  denote the jth description of access unit i, with 0&lt;=j&lt;N i  and 0&lt;=i&lt;A. For example, consider  FIG. 9 . All access units have 3 descriptions except access unit i+2, which has only 2 (i.e., N I =3 for all I different than (i+2) and N i+2 =2). The vector of running constraints is defined as xc=[R(i)], where R(i) is the available channel rate at time i, in this exemplary embodiment. The running constraints vector may contain many more elements in alternate embodiments of the present disclosure. 
   The method of this preferred embodiment is composed of two parts: First we identify the description properties and suggest a method to compute their values. Next we suggest a method for a media server to efficiently use these properties given the current running constraints. 
   For the Description Properties, the vector of description properties is defined as p=[S, alpha], where S is the size in bytes of the description and alpha is a weighting factor taking possibly discrete values in the interval [−1 1], where the deviation is denoted in source distortion. We assume that the source distortion of a description at time i can be zero but cannot be more than twice as much as the distortion of a description at time i−1 in this example. The description properties vector may contain many more elements in alternate embodiments. In addition, the computation of alpha here and below is also merely exemplary. 
   The computation of the size S is straightforward. The computation of alpha (see  FIG. 10 ) is as follows: Let the Mean Square Error (MSE) of description D i   j  be represented by MSE(D i   j ). For every access unit i, we compute the MSE distortion of every description 0&lt;=j&lt;N i  of access unit i given any previous descriptions 0&lt;=j&lt;N i−1  of access unit i−1. We define MSE(D −1   j )=100 for all 0&lt;=j&lt;N 0 , and N −1 =1. We initialize MSE(D −1   j )=100 for all 0&lt;=j&lt;N −1 , and N −1 =1. We then compute N i x N i−1  values for every access unit i. We denote these distortions by MSE(D i   j )(k), where k ranges from 0 to N i−1 . Next, we compute the parameter alpha i   j (k) by:
 
alpha i   j ( k )= MSE ( D   i   j )( k )/ MSE ( D   i−1   j )−1  (1)
 
with k such that 0&lt;=k&lt;N i−1  and MSE(D i−1   j )=max k  (MSE(D i−1   j )(k)).
 
   Therefore a description is fully described by 1+N i ×N i     —     1  values, which are stored as side information (i.e. metadata). 
   For the Media Server, streaming media over the standard protocol RTP/RTCP is considered. The media server periodically receives an RTCP Receiver Report message that contains an evaluation of both the packet loss ratio and the round-trip time the connection experiences. We denote by rho and RTT this packet loss ratio and round-trip time, respectively. We compute R(i) as:
 
 R ( i )=(1.3× MTU )/( RTT× sqrt( rho ))  (2)
 
   where MTU is the packet size being used on the connection. At every access unit time instant i, the media server knows the description that has been selected at time i−1. We denote by k the index of this description. It then computes N i  distortion values D i   j  by D i   j =D i−1   k (1+alpha i   k ). Finally the media server selects description k* at time i with the minimum distortion and such that the size S i   k*  is lower than or equal to R(i)×Delta. 
   Accordingly, rate adaptation via access unit skipping is covered by the present disclosure, embodiments of which create an extra null description for all skippable access units. Preferred embodiment implementations of the present invention fully comply with the MPEG-4 family of standards, and may thereby be applied directly to MP4 client players such as Quicktime 6.0, the IBM JAVA player and Real One. 
   These and other features and advantages of the present disclosure may be readily ascertained by one of ordinary skill in the pertinent art based on the teachings herein. It is to be understood that the teachings of the present disclosure may be implemented in various forms of hardware, software, firmware, special purpose processors, or combinations thereof. 
   The teachings of the present disclosure may be implemented as a combination of hardware and software. Moreover, the software is preferably implemented in firmware tangibly embodied on a program storage unit. The software may be uploaded to, and executed by, a machine comprising any suitable architecture. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units (“CPU”), a random access memory (“RAM”), and input/output (“I/O”) interfaces. The computer platform may also include an operating system and microinstruction code. The various processes and functions described herein may be either part of the microinstruction code or part of the software, or any combination thereof, which may be executed by the hardware. In addition, various other peripheral units may be connected to the computer platform such as an additional data storage unit. 
   It is to be further understood that, because some of the constituent system components and methods showed in the accompanying drawings are preferably implemented in software, the actual connections between the system components or the process function blocks may differ depending upon the manner in which the present disclosure is programmed. Given the teachings herein, one of ordinary skill in the pertinent art will be able to contemplate these and similar implementations or configurations of the present disclosure. 
   Although the illustrative embodiments have been described herein with reference to the accompanying drawings, it is to be understood that the present disclosure is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one of ordinary skill in the pertinent art without departing from the scope or spirit of the present disclosure. All such changes and modifications are intended to be included within the scope of the present disclosure as set forth in the appended claims.