Abstract:
In one embodiment of the present invention, a quality trainer and quality calculator collaborate to establish a consistent perceptual quality metric via machine learning. In a training phase, the quality trainer leverages machine intelligence techniques to create a perceptual quality model that combines objective metrics to optimally track a subjective metric assigned during viewings of training videos. Subsequently, the quality calculator applies the perceptual quality model to values for the objective metrics for a target video, thereby generating a perceptual quality score for the target video. In this fashion, the perceptual quality model judiciously fuses the objective metrics for the target video based on the visual feedback processed during the training phase. Since the contribution of each objective metric to the perceptual quality score is determined based on empirical data, the perceptual quality score is a more accurate assessment of observed video quality than conventional objective metrics.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention relate generally to computer science and, more specifically, to techniques for predicting perceptual video quality. 
         [0003]    2. Description of the Related Art 
         [0004]    Efficiently and accurately encoding source video is essential for real-time delivery of video content. After the encoded video content is received, the source video is decoded and viewed or otherwise operated upon. Some encoding processes employ lossless compression algorithms, such as Huffman coding, to enable exact replication of the source. By contrast, to increase compression rates and/or reduce the size of the encoded video content, other encoding processes leverage lossy data compression techniques that eliminate selected information, typically enabling only approximate reconstruction of the source. Further distortion may be introduced during resizing operations in which the video is scaled-up to a larger resolution to match the dimensions of a display device. 
         [0005]    Manually verifying the quality of delivered video is prohibitively time consuming. Consequently, to ensure an acceptable video watching experience, efficiently and accurately predicting the quality of delivered video is desirable. Accordingly, automated video quality assessment is often an integral part of the encoding and streaming infrastructure—employed in a variety of processes such as evaluating encoders and fine-tune streaming bitrates to maintain video quality. 
         [0006]    In one approach to assessing the quality of encoded videos, a full-reference quality metric, such as peak signal-to-noise ratio (PSNR), is used to compare the source video to the encoded video. However, while such metrics accurately reflect signal fidelity (i.e., the faithfulness of the encoded video to the source video), these metrics do not reliably predict human perception of quality. For example, fidelity measurements typically do not reflect that visual artifacts in still scenes are likely to noticeably degrade the viewing experience more than visual artifacts in fast-motion scenes. Further, due to such perceptual effects, such fidelity metrics are content-dependent and, therefore, inconsistent across different types of video data. For example, fidelity degradation in action movies that consist primarily of fast-motion scenes is less noticeable than fidelity degradation in slow-paced documentaries. 
         [0007]    As the foregoing illustrates, what is needed in the art are more effective techniques for predicting the perceived quality of videos. 
       SUMMARY OF THE INVENTION 
       [0008]    One embodiment of the present invention sets forth a computer-implemented method for estimating perceptual video quality. The method includes selecting a set of objective metrics that represent a plurality of deterministic video characteristics; for each training video included in a set of training videos, receiving a data set that describes the training video, where the data set includes a subjective value for a perceptual video quality metric and a set of objective values for the set of objective metrics; from the data sets, deriving a composite relationship that determines a value for the perceptual video quality metric based on a set of values for the set of objective metrics; for a target video, calculating a first set of values for the set of objective metrics; and applying the composite relationship to the first set of values to generate an output value for the perceptual video quality metric. 
         [0009]    One advantage of the disclosed techniques for estimating perceptual video quality is that the composite relationship that defines the perceptual video quality metric fuses objective metrics based on direct, human observations. More specifically, because human feedback for a set of training videos guides the contribution of each of the objective metrics, applying the composite relationship to target videos generalizes human feedback. Consequently, the perceptual video quality metric reliably predicts perceived video quality. By contrast, conventional quality metrics typically measure signal fidelity—a characteristic that does not necessarily track video quality as perceived by human vision systems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0011]      FIG. 1  is a conceptual illustration of a system configured to implement one or more aspects of the present invention; 
           [0012]      FIG. 2  is a block diagram illustrating the objective metric generation subsystem and the perceptual quality trainer of  FIG. 1 , according to one embodiment of the present invention; 
           [0013]      FIG. 3  is a block diagram illustrating the objective metric generation subsystem and the perceptual quality calculator of  FIG. 1 , according to one embodiment of the present invention; 
           [0014]      FIG. 4  is a flow diagram of method steps for predicting perceptual visual quality, according to one embodiment of the present invention; and 
           [0015]      FIG. 5  is a flow diagram of method steps for calculating values for a perceptual visual quality score based on an empirically trained model, according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    In the following description, numerous specific details are set forth to provide a more thorough understanding of the present invention. However, it will be apparent to one of skilled in the art that the present invention may be practiced without one or more of these specific details.
       System Overview       
 
         [0018]      FIG. 1  is a conceptual illustration of a system  100  configured to implement one or more aspects of the present invention. As shown, the system  100  includes a virtual private cloud (i.e., encapsulated shared resources, software, data, etc.)  102  connected to a variety of devices capable of transmitting input data and/or displaying video. Such devices include, without limitation, a desktop computer  102 , a smartphone  104 , and a laptop  106 . In alternate embodiments, the system  100  may include any number and/or type of input, output, and/or input/output devices in any combination. 
         [0019]    The virtual private cloud (VPC)  100  includes, without limitation, any number and type of compute instances  110 . The VPC  100  receives input user information from an input device (e.g., the laptop  106 ), one or more computer instances  110  operate on the user information, and the VPC  100  transmits processed information to the user. The VPC  100  conveys output information to the user via display capabilities of any number of devices, such as a conventional cathode ray tube, liquid crystal display, light-emitting diode, or the like. 
         [0020]    In alternate embodiments, the VPC  100  may be replaced with any type of cloud computing environment, such as a public or a hybrid cloud. In other embodiments, the system  100  may include any distributed computer system instead of the VPC  100 . In yet other embodiments, the system  100  does not include the VPC  100  and, instead, the system  100  includes a single computing unit that implements multiple processing units (e.g., central processing units and/or graphical processing units in any combination). 
         [0021]    As shown for the compute instance  110   0 , each compute instance  110  includes a central processing unit (CPU)  112 , a graphics processing unit (GPU)  114 , and a memory  116 . In operation, the CPU  112  is the master processor of the compute instance  110 , controlling and coordinating operations of other components included in the compute instance  110 . In particular, the CPU  112  issues commands that control the operation of the GPU  114 . The GPU  114  incorporates circuitry optimized for graphics and video processing, including, for example, video output circuitry. In various embodiments, GPU  114  may be integrated with one or more of other elements of the compute instance  110 . The memory  116  stores content, such as software applications and data, for use by the CPU  112  and the GPU  114  of the compute instance  110 . 
         [0022]    In general, the compute instances  110  included in the VPC  100  are configured to implement one or more applications. As shown, compute instances  110   1 - 110   N  are configured as an encoder  120 . The encoder  120  implements any type of data compression techniques as known in the art and in any technically feasible fashion. In some embodiments, the encoder  140  is a parallel chunk encoder that partitions the source data into multiple chunks and then performs data compression techniques concurrently on the chunks. 
         [0023]    To comply with resource constraints, such as encoded data size limitations and available streaming bandwidth, the encoder  120  implements lossy data compression techniques that eliminate selected information. By eliminating information, the encoder  120  creates “compression” artifacts that introduce distortions when the source data is reconstructed. The visual quality of the reconstructed source data is often further compromised by other elements included in the transcoding pipeline (i.e., the applications that translate the source data in one format to the reconstructed data in another format). For example, “scaling” artifacts may be introduced during the process of down-scaling and encoding the source data and then up-scaling the decoded data to the source resolution at the display device. 
         [0024]    To ensure an acceptable viewing experience, the quality of the reconstructed data and, indirectly, the caliber of the elements included in the transcoding pipeline are typically evaluated at various points in the design and delivery process using quality metrics. The values for the quality metrics are then used to guide the development of applications (e.g., encoders) and the real-time optimization of content delivery, such as stream-switching algorithms that are quality-aware. 
         [0025]    Many widely applied quality metrics (e.g., mean-squared-error (MSE) and peak signal-to-noise ratio (PSRN)) measure fidelity—the faithfulness of the reconstructed data to the source data. However, fidelity measurements do not reflect psycho-visual phenomena affecting the human visual system (HVS) such as masking, contrast sensitivity, or the highly structured content in natural images. Further, due to such imperfectly reflected perceptual effects, such fidelity metrics are content-dependent—the values are not comparable across different types of video data. For instance, video with grain noise is relatively heavily penalized in PSNR although the visual impact detectable by human viewers is relatively low. In general, conventional quality metrics are not a reliable indication of the visual quality as perceived by humans and, therefore, the acceptability of the viewing experience. 
         [0026]    For this reason, one or more of the compute instances  110  in the VPC  102  implement machine learning techniques to institute a consistent perceptual quality metric. Notably, a perceptual quality score  165  (i.e., value for the perceptual quality metric) correlates in a universal manner to subjective human visual experience irrespective of the type of video content. Any type of learning algorithm as known in the art may be leveraged to implement the consistent perceptual quality metric. In some embodiments, a support vector machine (SVM) provides the framework for the consistent perceptual quality metric. In other embodiments, a neural network implements the algorithms to establish the consistent perceptual quality metric. 
         [0027]    In a training phase, depicted in  FIG. 1  with dotted lines, a perceptual quality trainer  150  creates a perceptual quality model  155 . The perceptual quality model  155  is a supervised learning model that combines objective metrics  145  to optimally track the values for the subjective metric  135  assigned during viewings of training data. The objective metric subsystem  140  generates the objective metrics  145  based on comparison operations between the training data and the corresponding encoded training data. Such objective metrics  145  are referred to as full-reference quality indices, and may be generated in any technically feasible fashion. After a decoder  125  generates reconstructed training data from the encoded training data, viewers  110  watch the reconstructed data on display devices, such as the screen of the laptop  106 , and personally rate the visual quality—assigning values to the subjective metric  135 . 
         [0028]    The perceptual quality trainer  150  receives the calculated values for the objective metrics  145  and the human-assigned values for the subjective metric  135 . The perceptual quality trainer  150  then trains the perceptual quality model  155  based on these metrics. More specifically, the perceptual quality trainer  150  executes learning algorithms that recognize patterns between the objective metrics  145  and the subjective metric  135 . Subsequently, the perceptual quality trainer  150  configures the perceptual quality model  155  to fuse values for the objective metrics  145  into a perceptual quality score  165  that reflects the value for the subjective metric  135  and, consequently, the experience of the viewers  110 . 
         [0029]    In a scoring phase, depicted in  FIG. 1  with solid lines, a perceptual quality calculator  160  receives the perceptual quality model  155  and the values for the objective metrics  145  for target data. The perceptual quality calculator  160  applies the perceptual quality model  155  to the values for the objective metrics  145  and generates the perceptual quality score  165  for the target data. The values for the objective metrics  145  may be generated in any technically feasible fashion. For example, the objective metric subsystem  140  may compare any reference data (e.g., source data) to any derived target data (e.g., encoded source data) to calculate the values for the objective metrics  145 .
       Training Phase       
 
         [0031]      FIG. 2  is a block diagram illustrating the objective metric generation subsystem  140  and the perceptual quality trainer  150  of  FIG. 1 , according to one embodiment of the present invention. The objective metric generation subsystem  140  may be implemented in any technically feasible fashion and may include any number of separate applications that each generates any number of values for the objective metrics  145 . The perceptual quality trainer  150  includes, without limitation, a support vector machine (SVM) model generator  240  and a temporal adjustment identifier  250 . 
         [0032]    Upon receiving training data  205  and encoded training data  295  for a set of training videos, the objective metric generation subsystem  140  computes the values for the objective metrics  145 . The training videos may include any number and length of video clips that represent the range of video types to be represented by the perceptual quality score  165 . For example, in one embodiment the video clips in the training set span a diverse range of high level features (e.g., animation, sports, indoor, camera motion, face close-up, people, water, obvious salience, object number) and low level characteristics (e.g. film grain noise, brightness, contrast, texture, motion, color variance, color richness, sharpness). 
         [0033]    In some embodiments the set of training videos is the MCL-V video database of video clips that is available publically from the University of Southern California. In other embodiments, the ML-V video database of video clips is supplemented with selected high film grain clips and animation titles to increase the diversity and the robustness of the set of training videos. The training data  205  includes the training videos and the encoded training data  295  is derived from the training data  205 . More specifically, for each of the clips included in the training data  205 , the encoder  150  is configured to encode the clip repeatedly, at a variety of different resolutions and/or quality levels (i.e., bitrates). In this fashion, a predetermined number of encoded clips are generated from each video clip in the training set and these encoded clips form the encoded training data  295 . 
         [0034]    In general, each video quality metric exhibits both strengths and weaknesses. To leverage the strengths and mitigate the weaknesses, the objective metric generation subsystem  140  is configured to calculate a set of the objective metrics  145  that, together, provide valuable insight into the visual quality across the range of the encoded training data  295 . The selection of the objective metrics  145  may be made in any technically feasible fashion to address any number of anticipated artifacts. For instance, in some embodiments, the objective metrics  145  are empirically selected to assess degradation caused by compression (i.e., blockiness) and scaling (i.e. blurriness). 
         [0035]    As shown, the objective metrics  145  include a detail loss measure (DLM)  242 , a visual information fidelity (VIF)  244 , and an anti-noise signal-to-noise ratio (ANSNR)  246 . The DLM  242  is based on applying wavelet decomposition to identify the blurriness component of signals. The DLM  242  is relatively good at detecting blurriness in intermediate quality ranges, but is relatively poor at discriminating quality in higher quality ranges. The VIF  244  is based on applying a wavelet transformation to analyze signals in the frequency domain. The VIF  244  is relatively good at detecting slight bluing artifacts, but is relative poor at detecting blocking artifacts. 
         [0036]    The ANSNR  246  is designed to mitigate some drawbacks of SNR for film content. Prior to performing the SNR calculation, the objective metric generation subsystem  140  applies a weak low-pass filter to the training data  205  and a stronger low-pass filter to the encoded training data  295 . The ANSNR  246  is relatively fast to compute and good for detecting compression artifacts and strong scaling artifacts. However, the ANSNR  246  ignores slight blurring artifacts and, consequently, is not sensitive to minor quality changes in the high quality ranges. 
         [0037]    As a further optimization, since the human visual system is less sensitive to degradation during periods of high motion, the objective metric generation subsystem  140  computes motion values  248 . For each frame, the object metric generation subsystem  140  computes the motion value  248  as the mean co-located pixel difference of the frame with respect to the previous frame. Notably, to reduce the likelihood that noise is misinterpreted as motion, the object metric generation subsystem  140  applies a low-pass filter before performing the difference calculation. 
         [0038]    The values for the subjective metric  135  are assigned by the viewers  110  after watching the training data  205  and decoded versions of the encoded training data  295 , referred to herein as reconstructed training data, on any number and type of display devices. In one embodiment, each of the viewers  110  watch each training clip side-by-side with each of the reconstructed training clips and assigns values to the subjective metric  135 . The value for the subjective metric  135  is an absolute value that indicates the perceived visual quality. For instance, in one embodiment, the value for the subjective metric  135  may vary from 0 through 100. A score of 100 indicates that the reconstructed training clip appears identical to the training clip. A score below 20 indicates that the reconstructed training clip loses significant scene structure and exhibits considerable blurring relative to the training clip. 
         [0039]    Subsequently, the SVM model generator  240  receives the motion values  248 , values for the objective metrics  145 , and values for the subjective metric  135  for the encoded training data  295 . The SVM model generator  240  then applies learning algorithms to train the perceptual quality model  150 . For the encoded training data  295 , the SMV model generator  240  identifies correlations between the observed values for the subjective metric  135  and the calculated values for the objective metrics  145  as well as the motion values  248 . The SVM model generator  240  then generates the perceptual quality model  155 —a fusion of the objective metrics  135  and the motion value  248  that estimates the subjective metric  135 . As persons skilled in the art will recognize, the SVM model generator  240  may implement any of a number of learning algorithms to generate any type of model. In alternate embodiments, the SVM model generator  240  may be replaced with any processing unit that implements any type of learning algorithm, such as a neural network. 
         [0040]    The temporal adjustment identifier  250  is configured to tune the perceptual quality model  155  for corner cases. Notably, for very high motion scenes (i.e., high motion values  248 ), the perceptual quality model  155  may not adequately represent temporal masking effects. Consequently, the temporal adjustment identifier  250  generates a temporal adjustment  255  that is applied to the perceptual quality model  155  for such scenes. In some embodiments, the temporal adjustment  255  includes a threshold and a percentage. The temporal adjustment  255  is applied in conjunction with the perceptual quality model  155 , increasing the perceptual quality score  165  computed via the perceptual quality model  155  by the percentage.
       Scoring Phase       
 
         [0042]      FIG. 3  is a block diagram illustrating the objective metric generation subsystem  140  and the perceptual quality calculator  160  of  FIG. 1 , according to one embodiment of the present invention. As shown, the perceptual quality calculator  150  includes, without limitation, a support vector machine (SVM) mapper  360  and a temporal adjuster  370 . The perceptual quality calculator  150  operates during the scoring phase—computing perceptual quality scores  165  for the encoded data  195  that is derived from the source data  105  based on the “trained” perceptual quality model  155  and the temporal adjustment  255 . 
         [0043]    The SVM mapper  360  may be configured with any number of perceptual quality models  155  and temporal adjustments  255  that correspond to any number of training data  105 . In some embodiments, a model selection module (not shown) classifies training data  105  of similar content into groups and then assigns the perceptual quality model  155  based on the content of the encoded data  195  to be assessed. For example, one set of training data  105  may include relatively high quality videos and, therefore, the corresponding perceptual quality model  155  is optimized to determine the perceptual quality score  165  for high quality encoded data  195 . By contrast, another set of training data  105  may include relatively low quality videos and, therefore, the corresponding perceptual quality model  155  is optimized to determine the perceptual quality score  165  for low quality encoded data  195 . 
         [0044]    Upon receiving the source data  105  and the encoded data  195  derived from the source data  105 , the objective metric generation subsystem  140  computes the values for the objective metrics  145  and the motion values  248 . In general, the values for the objective metrics  145  and the motion values  248  may be determined in any technically feasible fashion. For instance, some embodiments include multiple objective metric calculators, and each objective metric calculator configures a different objective metric. 
         [0045]    The SVM mapper  360  applies the perceptual quality model  155  to the objective metrics  145  and the motion values  248  to generate a perceptual quality score  165 . Subsequently, the temporal adjuster  370  selectively applies the temporal adjustment  255  to the perceptual quality score  165  to fine-tune corner cases. In one embodiment, the temporal adjuster  370  compares the motion values  240  to a threshold included in the temporal adjustment  255 . If the motion value  240  exceeds the threshold, then the temporal adjuster  370  increases the perpetual quality score  165  by a percentage included in the temporal adjustment  255  to reflect the inherent pessimism of the perceptual quality model  155  for high motion scenes. Because the perceptual quality model  155  and the temporal adjustment  255  track quality observed by the viewers  110 , the perceptual quality score  165  reflects the quality of the encoded data  185  when viewed by humans. 
         [0046]    Note that the techniques described herein are illustrative rather than restrictive, and may be altered without departing from the broader spirit and scope of the invention. In particular, the perceptual quality trainer  150  may be replaced with any module that implements any number of machine learning processes to generate a model that fuses multiple objectively calculated values to track an experimentally observed visual quality. Correspondingly, the perceptual quality calculator  160  may be replaced with any module that applies the model in a consistent fashion. Further, the perceptual quality trainer  150  may include any number of adjustment identification modules designed to fine-tune the generated model, and the perceptual quality calculator  160  may include any number of adjustment calculators that apply the identified adjustments. 
         [0047]    The granularity (e.g., per frame, per scene, per shot, per 6 minute clip, etc.) of the training data  105 , the objective metrics  145 , the subjective metrics  135 , and the motion values  245  may be vary within and between implementations. As persons skilled in the art will recognize, conventional mathematical techniques (e.g., averaging, extrapolating, interpolating, maximizing, etc.) may be applied to the objective metrics  145 , the subjective metrics  135 , and/or the motion values  245  in any combination to ensure measurement unit consistency. Further, the perceptual quality trainer  150  and the perceptual quality calculator  160  may be configured to determine the perceptual quality model  155 , the temporal adjustment  255 , and/or the perceptual quality score  160  at any granularity.
       Predicting Human-Perceived Quality       
 
         [0049]      FIG. 4  is a flow diagram of method steps for predicting perceptual visual quality, according to one embodiment of the present invention. Although the method steps are described with reference to the systems of  FIGS. 1-3 , persons skilled in the art will understand that any system configured to implement the method steps, in any order, falls within the scope of the present invention. 
         [0050]    As shown, a method  400  begins at step  404 , where the perceptual quality trainer  150  receives the training data  205 . The training data  205  may include any number and length of video clips. For example, in one embodiment the training data  205  includes sixteen six minute clips. At step  406 , the encoder  120  derives the encoded test data  295  from the training data  205  for any number of resolutions and combination of bit rates. In general, the resolutions and bit rates are selected to reflect target supported ranges for viewing devices and/or streaming bandwidth. 
         [0051]    At step  406 , the perceptual quality trainer  150  receives values for the subjective metric  135  for reconstructed video clips ((i.e., decoded, scaled, etc.) derived from the encoded training data  295 . The perceptual quality trainer  150  may obtain values for the subjective metric  135  in any form and may perform any number of post-processing operations (e.g., averaging, removal of outlying data points, etc.). In alternate embodiments, the perceptual quality trainer  150  may receive and process data corresponding to any number of subjective metrics  135  in any technically feasible fashion. 
         [0052]    For example, in some embodiments, the perceptual quality trainer  150  receives feedback generated during a series of side-by-side, human (e.g., by the viewers  100 ) comparisons of the training data  205  and the reconstructed video clips (i.e., decoded, scaled, etc.) derived from the encoded training data  295 . For each of the reconstructed video clips, the feedback includes a value for the subjective metric  135  for the corresponding encoded test data  295 . The value of the subjective metric  135  reflects the average observed visual quality based on an absolute, predetermined, quality scale (e.g., 0-100, where 100 represents no noticeable artifacts). 
         [0053]    At step  410 , the objective metric generation subsystem  140  computes values for the objective metrics  145  for the encoded test data  295  based on both the encoded test data  295  and the training data  205 . The objective metric generation subsystem  140  may select the objective metrics  145  and then compute the values for the objective metrics  145  in any technically feasible fashion. For example, in some embodiments the objective metric generation subsystem  140  is configured to compute values for the detail loss measure (DLM)  242 , the visual information fidelity (VIF)  244 , and the anti-noise signal-to-noise ratio (ANSNR)  246 . 
         [0054]    As part of step  410 , the objective metric generation subsystem  140  may also compute any other type of spatial or temporal data associated with the encoded test data  295 . In particular, the objective metric generation subsystem  140  calculates the motion values  248  for each frame included in the encoded test data  295 —the temporal visual difference. 
         [0055]    At step  412 , the support vector machine (SVM) model generator  240  performs machine learning operations—training the perceptual quality model  155  to track the values for the subjective metric  135  based on a fusion of the values for the objective metrics  145  and the motion values  248 . At step  414 , the perceptual quality trainer  150  determines whether the perceptual quality model  155  accurately tracks the values for the subjective metric  135  during periods of high motion, If, at step  414 , the perceptual quality trainer  150  determines that the accuracy of the perceptual quality model  155  is acceptable, then this method proceeds directly to step  418 . 
         [0056]    If, at step  414 , the perceptual quality trainer  150  determines that the accuracy of the perceptual quality model  155  is unacceptable, then this method proceeds to step  416 . At step  416 , the temporal adjustment identifier  250  determines a threshold beyond which the perceptual quality score  165  computed based on the perceptual quality model  155  is unacceptably pessimistic. The temporal adjustment identifier  250  also determines a percentage increase that, when applied to the perceptual quality score  165  computed based on the perceptual quality model  155 , improves the accuracy of the perceptual quality score  165 . Together, the threshold and the percentage increase form the temporal adjustment  255 . 
         [0057]    At step  418 , the perceptual quality calculator  160  calculates the perceptual quality scores  165  for the encoded data  195  based on the perceptual quality model  165  and, when present, the temporal adjustment  255 . In general, the perceptual quality calculator  160  computes the perceptual quality score  165  by applying the perceptual quality model  155  to the values for the objective metrics  155  and the motion values  248  for the encoded data  195  in any technically feasible fashion. 
         [0058]    For example, in some embodiments, the perceptual quality calculator  150  performs the method steps outlined below in conjunction with  FIG. 5 —leveraging the trained perceptual quality model  155  to obtain perceptual quality scores  165  (i.e., values of the subjective metric  135 ). Notably, during the training phase the perceptual quality model  165  directly incorporates human feedback for the training data  205 . Subsequently, during the scoring phase the trained perceptual quality model  165  enables the generalization of this human feedback to any number and type of source data  105 . 
         [0059]      FIG. 5  is a flow diagram of method steps for calculating values for a perceptual visual quality score based on an empirically trained model, according to one embodiment of the present invention. Although the method steps are described with reference to the systems of  FIGS. 1-3 , persons skilled in the art will understand that any system configured to implement the method steps, in any order, falls within the scope of the present invention. 
         [0060]    As shown, a method  500  begins at step  516 , where the perceptual quality calculator  160  receives the perceptual quality model  155  and the temporal adjustment  255 . In alternate embodiments, the temporal adjustment  255  may be omitted. In other embodiments, the temporal adjustment  255  is replaced with any number of other adjustments that are designed to fine-tune the perceptual quality score  165 . The perceptual quality model  155  may be generated in any technically feasible fashion. For example, in some embodiments, the perceptual quality trainer  140  performs the method steps  406 - 416  outlined in  FIG. 4 . 
         [0061]    At step  518 , the perceptual quality calculator  160  receives the source data  105 . At step  520 , the encoder  120  derives the encoded data  195  from the source data  205  for a target resolution and/or bit rate. At step  522 , the objective metric generation subsystem  140  computes values for the objective metrics  145  for the encoded data  195  based on the encoded data  195  and, for optionally, the source data  105 . The objective metric generation subsystem  140  also computes the motion values  248  for each frame of the encoded data  195 . In general, the perceptual quality calculator  160  is configured to calculator the values for the independent variables in the perceptual quality model  155 . 
         [0062]    At step  524 , the support vector machine (SVM) mapper  360  applies the perceptual quality model  155  to the values for the objective metrics  145  and the motion values  248  for the encoded data  195  to generate the perceptual quality score  165 . At step  526 , the temporal adjuster  370  determines whether the motion values  248  of one or more frames exceed the threshold specified in the temporal adjustment  255 . If, at step  526 , the temporal adjuster  370  determines that none of the motion values  248  exceed the threshold, then the perceptual quality calculator  160  considers the perceptual quality score  165  to accurately predict the expected viewing experience and the method  500  ends. 
         [0063]    If, at step  526 , the temporal adjuster  370  determines that any of the motion values  248  exceed the threshold, then the temporal adjuster  370  considers the frames to reflect a period of high motion, and the method  500  proceeds to step  526 . At step  526 , the temporal adjuster  370  increases the perceptual quality score  165  by a threshold percentage (specified in the temporal adjustment  255 ) to compensate for the pessimism of the perceptual quality model  155  during periods of high motion, and the method  500  ends. 
         [0064]    In sum, the disclosed techniques may be used to efficiently and reliably predict perceptual video quality. A perceptual quality trainer implements a support vector machine (SVM) to generate a perceptual quality model. Notably, for a training set of videos, the SVM is configured to fuse values for a set of objective metrics and temporal motion into a perceptual quality score—a subjective visual quality score that is based on human video-viewing feedback. Subsequently, a perceptual quality calculator applies the perceptual quality model to values for the objective metrics and temporal motion for target videos to generate corresponding values for the perceptual quality metric (i.e., visual quality score). 
         [0065]    Advantageously, training the perceptual quality model using direct observations made by human visual systems enables the perceptual quality calculator to efficiently calculate quality scores that reliably predict perceived video quality in an absolute manner . By contrast, conventional quality metrics typically measure signal fidelity—a content-dependent, inconsistent, and unreliable indication of real world viewing appreciation. Further, by separating the initial empirically-based training phase from the subsequent per-video deterministic calculation phase, the disclosed techniques are expeditious and scalable. Consequently the perceptual quality model both reduces the time required to develop and accurately evaluate encoders and enables time-sensitive encoding applications, such as real-time quality-aware stream-switching. 
         [0066]    The descriptions of the various embodiments have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. 
         [0067]    Aspects of the present embodiments may be embodied as a system, method or computer program product. Accordingly, aspects of the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. 
         [0068]    Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. 
         [0069]    Aspects of the present disclosure are described above with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, enable the implementation of the functions/acts specified in the flowchart and/or block diagram block or blocks. Such processors may be, without limitation, general purpose processors, special-purpose processors, application-specific processors, or field-programmable 
         [0070]    The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
         [0071]    While the preceding is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.