Patent Document

RELATED APPLICATIONS 
     This application claims priority to “Systems, Methods, and Apparatus for Real-Time High Definition Encoding”, U.S. Provisional Application for Patent, Ser. No. 60/681,268, filed May 16, 2005. 
    
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     [Not Applicable] 
     MICROFICHE/COPYRIGHT REFERENCE 
     [Not Applicable] 
     BACKGROUND OF THE INVENTION 
     Advanced Video Coding (AVC) (also referred to as H.264 and MPEG-4, Part 10) can be used to compress video content for transmission and storage, thereby saving bandwidth and memory. However, encoding in accordance with AVC can be computationally intense. 
     In certain applications, for example, live broadcasts, it is desirable to compress high definition television content in accordance with AVC in real time. However, the computationally intense nature of AVC operations in real time may exhaust the processing capabilities of certain processors. Parallel processing may be used to achieve real time AVC encoding, where the AVC operations are divided and distributed to multiple instances of hardware which perform the distributed AVC operations, simultaneously. 
     Ideally, the throughput can be multiplied by the number of instances of the hardware. However, in cases where a first operation is dependent on the results of a second operation, the first operation may not be executable simultaneously with the second operation. In contrast, the performance of the first operation may have to wait for completion of the second operation. 
     AVC uses temporal coding to compress video data. Temporal coding divides a picture into blocks and encodes the blocks using similar blocks from other pictures, known as reference pictures. To achieve the foregoing, the encoder searches the reference picture for a similar block. This is known as motion estimation. At the decoder, the block is reconstructed from the reference picture. However, the decoder uses a reconstructed reference picture. The reconstructed reference picture is different, albeit imperceptibly, from the original reference picture. Therefore, the encoder uses encoded and reconstructed reference pictures for motion estimation. 
     Using encoded and reconstructed reference pictures for motion estimation causes encoding of a picture to be dependent on the encoding of the reference pictures. This is can be disadvantageous for parallel processing. 
     Additional limitations and disadvantages of conventional and traditional approaches will become apparent to one of ordinary skill in the art through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings. 
     BRIEF SUMMARY OF THE INVENTION 
     Presented herein are systems, methods, and apparatus for encoding video data in real time, as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims. 
     These and other advantages and novel features of the present invention, as well as illustrated embodiments thereof will be more fully understood from the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a block diagram of an exemplary system for encoding video data in accordance with an embodiment of the present invention; 
         FIG. 2  is a flow diagram for encoding video data in accordance with an embodiment of the present invention; 
         FIG. 3A  is a block diagram describing spatially predicted macroblocks; 
         FIG. 3B  is a block diagram describing temporally predicted macroblocks; 
         FIG. 4  is a block diagram describing the encoding of a prediction error; 
         FIG. 5  is a flow diagram for encoding video data in accordance with an embodiment of the present invention; 
         FIG. 6  is a block diagram describing the estimation of data for encoding pictures; 
         FIG. 7  is a block diagram of a system for encoding video data in accordance with an embodiment of the present invention; and 
         FIG. 8  is a block diagram describing an exemplary distribution of pictures in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , there is illustrated a block diagram of an exemplary system for encoding video data in accordance with an embodiment of the present invention. The video data comprises a plurality of pictures  115 ( 0 ) . . .  115 ( x ). The system comprises a plurality of encoders  110 ( 0 ) . . .  110 ( n ). The plurality of encoders  110 ( 0 ) . . .  110 ( n ) estimate amounts of data for encoding a corresponding plurality of pictures  115 ( 0 ) . . .  115 ( n ), in parallel. A master  105  generates a plurality of target rates corresponding to the pictures and the encoders. The encoders  110 ( 0 ) . . .  110 ( n ) lossy compress the pictures based on the corresponding target rates. 
     The master  105  can receive the video data for compression. Where the master  105  receives the video data for compression, the master  105  can divide the video data among the encoders  110 ( 0 ) . . .  110 ( n ), provide the divided portions of the video data to the different encoders, and play a role in controlling the rate of compression. 
     In certain embodiments, the compressed pictures are returned to the master  105 . The master  105  collates the compressed pictures, and either writes the compressed video data to a memory (such as a disc drive) or transmits the compressed video data over a communication channel. 
     The master  105  plays a role in controlling the rate of compression by each of the encoders  110 ( 0 ) . . .  110 ( n ). Compression standards, such as AVC, MPEG-2, and VC-1 use both lossless and lossy compression to encode video data  102 . In lossless compression, information from the video data is not lost from the compression. However, in lossy compression, some information from the video data is lost to improve compression. An example of lossy compression is the quantization of transform coefficients. 
     Lossy compression involves trade-off between quality and compression. Generally, the more information that is lost during lossy compression, the better the compression rate, but, the more the likelihood that the information loss perceptually changes the video data and reduces quality. 
     The encoders  110  perform a pre-encoding estimation of the amount of data for encoding pictures  115 . For example, the encoders  110  can estimate the amount of data for encoding a picture  115 , by estimating the amount of data for encoding the picture  115  with a given quantization parameter. 
     Based on the estimate of the amount of data for encoding the picture  115 , the master  105  can provide a target rate to the encoders  110  for compressing the picture  115 . The encoders  110 ( 0 ) . . .  110 ( n ) can adjust certain parameters that control lossy compression to achieve an encoding rate that is close, if not equal, to the target rate. 
     The estimate of the amount of data for encoding a picture  115  can be based on a variety of factors. These qualities can include, for example, content sensitivity, measures of complexity of the pictures and/or the blocks therein, and the similarity of blocks in the pictures to candidate blocks in reference pictures. Content sensitivity measures the likelihood that information loss is perceivable, based on the content of the video data. For example, in video data, human faces are likely to be more closely examined than animal faces. 
     In certain embodiments of the present invention, the master  105  can also collect statistics of past target rates and actual rates under certain circumstances. This information can be used as feedback to bias future target rates. For example, where the actual target rates have been consistently exceeded by the actual rates in the past under a certain circumstance, the target rate can be reduced in the future under the same circumstances. 
     Referring now to  FIG. 2 , there is illustrated a flow diagram for encoding video data in accordance with an embodiment of the present invention. At  205 , the encoders  110 ( 0 ) . . .  110 ( n ) each estimate the amounts of data for encoding pictures  115 ( 0 ) . . .  115 ( n ) in parallel. 
     At  210 , the master  105  generates target rates for each of the pictures  115 ( 0 ) . . .  115 ( n ) based on the estimated amounts during  205 . At  215 , the encoders  110 ( 0 ) . . .  110 ( n ) lossy compress the pictures  115 ( 0 ) . . .  115 ( n ) based on the target rates corresponding to the plurality of pictures. 
     Embodiments of the present invention will now be presented in the context of an exemplary video encoding standard, Advanced Video Coding (AVC) (also known as MPEG-4, Part 10, and H.264). A brief description of AVC will be presented, followed by embodiments of the present invention in the context of AVC. It is noted, however, that the present invention is by no means limited to AVC and can be applied in the context of a variety of the encoding standards. 
     Advanced Video Coding 
     Advanced Video Coding (also known as H.264 and MPEG-4, Part 10) generally provides for the compression of video data by dividing video pictures into fixed size blocks, known as macroblocks. The macroblocks can then be further divided into smaller partitions with varying dimensions. 
     The partitions can then be encoded, by selecting a method of prediction and then encoding what is known as a prediction error. AVC provides two types of predictors, temporal and spatial. The temporal prediction uses a motion vector to identify a same size block in another picture and the spatial predictor generates a prediction using one of a number of algorithms that transform surrounding pixel values into a prediction. Note that the data coded includes the information needed to specify the type of prediction, for example, which reference frame, partition size, spatial prediction mode etc. 
     The reference pixels can either comprise pixels from the same picture or a different picture. Where the reference block is from the same picture, the partition is spatially predicted. Where the reference block is from another picture, the partition is temporally predicted. 
     Spatial Prediction 
     Referring now to  FIG. 3A , there is illustrated a block diagram describing spatially encoded macroblocks  320 . Spatial prediction, also referred to as intra prediction, is used by H.264 and involves prediction of pixels from neighboring pixels. Prediction pixels are generated from the neighboring pixels in any one of a variety of ways. 
     The difference between the actual pixels of the partition  430  and the prediction pixels P generated from the neighboring pixels is known as the prediction error E. The prediction error E is calculated and encoded. 
     Temporal Prediction 
     Referring now to  FIG. 3B , there is illustrated a block diagram describing temporally prediction. With temporal prediction, partitions  430  are predicted by finding a partition of the same size and shape in a previously encoded reference frame. Additionally, the predicted pixels can be interpolated from pixels in the frame or field, with as much as ¼ pixel resolution in each direction. A macroblock  320  is encoded as the combination of data that specifies the derivation of the reference pixels P and the prediction errors E representing its partitions  430 . The process of searching for the similar block of predicted pixels P in pictures is known as motion estimation. 
     The similar block of pixels is known as the predicted block P. The difference between the block  430  and the predicted block P is known as the prediction error E. The prediction error E is calculated and encoded, along with an identification of the predicted block P. The predicted blocks P are identified by motion vectors MV and the reference frame they came from. Motion vectors MV describe the spatial displacement between the block  430  and the predicted block P. 
     Transformation, Quantization, and Scanning 
     Referring now to  FIG. 4 , there is illustrated a block diagram describing the encoding of the prediction error E. With both spatial prediction and temporal prediction, the macroblock  320  is represented by a prediction error E. The prediction error E is a two-dimensional grid of pixel values for the luma Y, chroma red Cr, and chroma blue Cb components with the same dimensions as the macroblock  320 , like the macroblock. 
     A transformation transforms the prediction errors E  430  to the frequency domain. In H.264, the blocks can be 4×4, or 8×8. The foregoing results in sets of frequency coefficients f 00  . . . f mn , with the same dimensions as the block. The sets of frequency coefficients are then quantized, resulting in sets of quantized frequency coefficients, F 00  . . . F mn . 
     Quantization is a lossy compression technique where the amount of information that is lost depends on the quantization parameters. The information loss is a tradeoff for greater compression. In general, the greater the information loss, the greater the compression, but, also, the greater the likelihood of perceptual differences between the encoded video data, and the original video data. 
     The pictures  115  are encoded as the portions  120  forming them. The video sequence is encoded as the frames forming it. The encoded video sequence is known as a video elementary stream. Transmission of the video elementary stream instead of the original video consumes substantially less bandwidth. 
     Due to the lossy compression, the quantization of the frequency components, there is a loss of information between the encoded and decoded (reconstructed) pictures  115  and the original pictures  115  of the video data. Ideally, the loss of information does not result in perceptual differences. As noted above, both spatially and temporally encoded pictures are predicted from predicted blocks P of pixels. When the spatially and temporally encoded pictures are decoded and reconstructed, the decoder uses blocks of reconstructed pixels P from reconstructed pictures. Predicting from predicted blocks of pixels P in original pictures can result in accumulation of information loss between both the reference picture  115  and the picture  115  to be predicted. Accordingly, during spatial and temporal encoding, the encoder uses predicted blocks P of pixels from reconstructed pictures  115 . 
     Motion estimating entirely from reconstructed pictures  115  creates data dependencies between the compression of the predicted picture  115  and the predicted picture  115 . This is particularly disadvantageous because exhaustive motion estimation is very computationally intense. 
     According to certain aspects of the present invention, the process of estimating the amount of data for encoding the pictures  115  can be used to assist and reduce the amount of time for compression of the pictures. This is especially beneficial because the estimations are performed in parallel. 
     Referring now to  FIG. 5 , there is illustrated a flow diagram for estimating the amount of data for encoding pictures in accordance with an embodiment of the present invention, when temporal prediction is used. The foregoing can be used in conjunction with spatially prediction from original pictures, such as that described in Provisional Application Ser. No. 60/681,642 by Chin, filed May 16, 2005. 
     The flow diagram will be described in conjunction with  FIG. 6 . The amount of data for encoding pictures is estimated in parallel during  505 - 515 , the motion estimation is performed during  520 , and the pictures are encoded during  525 - 530 . 
     At  505  original reference pictures  115 ORP are searched for candidate blocks CB that are similar to blocks  430  in the pictures. The original reference pictures  115 ORP includes pictures  115 , frames, top fields, bottom fields, or portions of the foregoing, from the video data received by the master  105 , frames, top fields, bottom fields, or portions of the foregoing, from the video data  102 , where the compression is data independent from the compression of other pictures  115 , frames, top fields, bottom fields, or portions of the foregoing. This can include, but is not limited to, scaled down versions of the pictures  115 , frames, top field, bottom, or portions thereof, from the video data  102 . 
     The blocks  430  can be any two-dimensional structure of pixels from a picture  115 , wherein each dimension is at least 2 pixels. The blocks  430  can also include a collection of blocks  430 , such as a macroblock  320 . The blocks  430  can also include pixels that are taken from a scaled down version of a picture  120 . 
     Searching a scaled down original reference picture  115 ORP with a block  430  from a scaled down picture  115  can significantly reduce the time for the search for candidate blocks CB. Additionally, the time can be further reduced by using larger blocks  430 . 
     At  510 , candidate blocks are selected based on a comparison between the candidate blocks CB and the blocks  430  in the pictures  115 . The degree of similarity between the candidate blocks CB and the blocks  430  can be measured in a variety of ways, such as the sum of absolute differences and the sum of absolute transformed differences. The blocks with the greatest similarity can be selected as the candidate blocks CB. 
     In a reconstructed reference pictures  115 RRP, the areas in the vicinity of areas corresponding to the candidate blocks CB in the original reference pictures  115 ORP are likely to provide suitable reference blocks P. Additionally, the comparison between the candidate block CB and the blocks  430  are likely to be indicative of the prediction error. Thus from the comparison between the candidate blocks CB in the original reference pictures  115  and the blocks  430  in the picture  115 , an estimate can be made of the amount of data for encoding the picture  115 . Accordingly, at  515 , the amount of data for encoding the pictures is estimated based on the comparisons between the candidate blocks in the original reference pictures  115 ORP and the blocks  430  in the picture  115 . 
     Because original reference pictures  115 ORP are used, in contrast to reconstructed reference pictures  115 RRP,  505 - 515  can be performed for separate pictures in parallel. Additionally, the candidate block CB information can be used for motion estimation. 
     At  520 , the areas in reconstructed reference pictures  115 RRP that are in the vicinity of the areas corresponding to the candidate blocks in the original reference picture  115 ORP can be searched for reference blocks P for the blocks  430  in the picture  115 . Additionally areas in the reconstructed reference picture  115 RRP can also be searched. Additional areas can also be searched based on candidate blocks for neighboring blocks  430 . For example, the areas can be similarly displaced from the block  430  to displacement between the candidate block CB for a neighboring block  430  and the neighboring block  430 . 
     The search for the reference blocks P can differ from  505  in a number of ways. For example, reconstructed reference picture  115 RRP and the picture  115  can be full scale, whereas during  505 , the original reference picture  115 ORP and the picture  115  can be reduced scale. Additionally, the blocks  430  can be smaller partitions of the blocks used in  505 . For example, during  505 , a 16×16 block can be used, while during  520 , the 16×16 block can be divided into smaller blocks, such as 8×8 blocks  430 ( 0 ) . . .  430 ( 3 ), or 4×4 blocks. Also, the reconstructed reference picture  115 RRP can be searched with ¼ pixel resolution. 
     At  525 , the target rate is generated for each picture  115 , based on the estimated amount of data for encoding the picture during  515 . At  530 , the pictures  115  are quantized using quantization parameters that are based on the target rate for the pictures provided during  525 . 
     Referring now to  FIG. 7 , there is illustrated a block diagram of an exemplary system  700  for encoding video data in accordance with an embodiment of the present invention. The system  700  comprises a picture rate controller  705 , a macroblock rate controller  710 , a pre-encoder  715 , hardware accelerator  720 , spatial from original comparator  725 , an activity metric calculator  730 , a motion estimator  735 , a mode decision and transform engine  740 , an arithmetic encoder  750 , and a CABAC encoder  755 . 
     The picture rate controller  705  can comprise software or firmware residing on the master  105 . The macroblock rate controller  710 , pre-encoder  715 , spatial from original comparator  725 , mode decision and transform engine  740 , spatial predictor  745 , arithmetic encoder  750 , and CABAC encoder  755  can comprise software or firmware residing on each of the encoders  110 ( 0 ) . . .  110 ( n ). The pre-encoder  715  includes a complexity engine  760  and a classification engine  765 . The hardware accelerator  720  can either be a central resource accessible by each of the encoders  110 , or decentralized hardware at the encoders  110 . 
     The hardware accelerator  720  can search the original reference pictures  115 ORP for candidate blocks CB that are similar to blocks  430  in the pictures  115  and compare the candidate blocks CB to the blocks  430  in the pictures. The pre-encoder  715  estimates the amount of data for encoding pictures  115 . 
     The pre-encoder  715  comprises a complexity engine  760  that estimates the amount of data of data for encoding the pictures  115 , based on the results of the hardware accelerator  720 . The pre-encoder  715  also comprises a classification engine  765 . The classification engine  765  classifies certain content from the pictures  115  that is perceptually sensitive, such as human faces, where additional data for encoding is desirable. 
     Where the classification engine  765  classifies certain content from pictures  115  to be perceptually sensitive, the classification engine  765  indicates the foregoing to the complexity engine  760 . The complexity engine  760  can adjust the estimate of data for encoding the pictures  115 . The complexity engine  765  provides the estimate of the amount of data for encoding the pictures by providing an amount of data for encoding the picture with a nominal quantization parameter Qp. It is noted that the nominal quantization parameter Qp is not necessarily the quantization parameter used for encoding pictures  115 . 
     The picture rate controller  705  provides a target rate to the macroblock rate controller  710 . The motion estimator  735  searches the vicinities of areas in the reconstructed reference picture that correspond to the candidate blocks CB, for reference blocks P that are similar to the blocks  430  in the plurality of pictures. 
     The search for the reference blocks P by the motion estimator  735  can differ from the search by the hardware accelerator  720  in a number of ways. For example, reconstructed reference picture  115 RRP and the picture  115  can be full scale, whereas the hardware accelerator  720  searches the original reference picture  115 ORP and the picture  115  that can be reduced scale. Additionally, the blocks  430  can be smaller partitions of the blocks by the hardware accelerator  720 . For example, the hardware accelerator  720  can use a 16×16 block, while the motion estimator  735  divides the 16×16 block into smaller blocks, such as 8×8 or 4×4 blocks. Also, the motion estimator  735  can search the reconstructed reference picture  115 RRP with ¼ pixel resolution. 
     The spatial predictor  745  performs the spatial predictions for blocks  430 . The mode decision &amp; transform engine  740  determines whether to use spatial encoding or temporal encoding, and calculates, transforms, and quantizes the prediction error E from the reference block. The complexity engine  760  indicates the complexity of each macroblock  320  at the macroblock level based on the results from the hardware accelerator  720 , while the classification engine  765  indicates whether a particular macroblock contains sensitive content. Based on the foregoing, the complexity engine  760  provides an estimate of the amount of bits that would be required to encode the macroblock  320 . The macroblock rate controller  710  determines a quantization parameter and provides the quantization parameter to the mode decision &amp; transform engine  740 . The mode decision &amp; transform engine  740  comprises a quantizer Q. The quantizer Q uses the foregoing quantization parameter to quantize the transformed prediction error. 
     The mode decision &amp; transform engine  740  provides the transformed and quantized prediction error E to the arithmetic encoder  750 . Additionally, the arithmetic encoder  750  can provide the actual amount of bits for encoding the transformed and quantized prediction error E to the picture rate controller  705 . The arithmetic encoder  750  codes the quantized prediction error E into bins. The CABAC encoder  755  converts the bins to CABAC encoded data. The actual amount of data for coding the macroblock  320  can also be provided to the picture rate controller  705 . 
     In certain embodiments of the present invention, the picture rate controller  705  can record statistics from previous pictures, such as the target rate given and the actual amount of data encoding the pictures. The picture rate controller  705  can use the foregoing as feedback. For example, if the target rate is consistently exceeded by a particular encoder, the picture rate controller  705  can give a lower target rate. 
     Referring now to  FIG. 8 , there is illustrated a block diagram of an exemplary distribution of pictures by the master  105  to the encoders  110 ( 0 ) . . .  110 ( x ). The master  105  can divide the pictures  115  into groups  820 , and the groups into sub-groups  820 ( 0 ) . . .  820 ( n ). Certain pictures, intra-coded pictures  115 I, are not temporally coded, certain pictures, predicted-pictures  115 P, are temporally encoded from one reconstructed reference pictures  115 RRP, and certain pictures, bi-directional pictures  115 B, are encoded from two or more reconstructed reference pictures  115 RRP. In general, intra-coded pictures  115 I take the least processing power to encode, while bi-directional pictures  115 B take the most processing power to encode. 
     In an exemplary case, the master  105  can designate that the first picture  115  of a group  820  is an intra-coded picture  115 I, every third picture, thereafter, is a predicted picture  115 P, and that the remaining pictures are bi-directional pictures  115 B. Empirical observations have shown that bi-directional pictures  115 B take about twice as much processing power as predicted pictures  115 P. Accordingly, the master  105  can provide the intra-coded picture  115 I, and the predicted pictures  115 P to one of the encoders  110 , as one sub-group  820 ( 0 ), and divide the bi-directional pictures  115 B among other encoders  110  as four sub-groups  820 ( 1 ) . . .  820 ( 4 ). 
     The encoders  110  can search original reference pictures  115 ORP for candidate blocks that are similar to blocks in the plurality of pictures, and select the candidate blocks based on comparison between the candidate blocks and the blocks in the pictures. The encoders  110  can then search the vicinity of an area in the reconstructed reference picture  115 RRP that corresponds to the area of the candidate blocks in the original reference picture  115 ORP for a reference block. 
     The embodiments described herein may be implemented as a board level product, as a single chip, application specific integrated circuit (ASIC), or with varying levels of the decoder system integrated with other portions of the system as separate components. 
     The degree of integration of the decoder system may primarily be determined by the speed and cost considerations. Because of the sophisticated nature of modern processor, it is possible to utilize a commercially available processor, which may be implemented external to an ASIC implementation. 
     If the processor is available as an ASIC core or logic block, then the commercially available processor can be implemented as part of an ASIC device wherein certain functions can be implemented in firmware. For example, the macroblock rate controller  710 , pre-encoder  715 , spatial from original comparator  725 , activity metric calculator  730 , motion estimator  735 , mode decision and transform engine  740 , arithmetic encoder  750 , and CABAC encoder  755  can be implemented as firmware or software under the control of a processing unit in the encoder  110 . The picture rate controller  705  can be firmware or software under the control of a processing unit at the master  105 . Alternatively, the foregoing can be implemented as hardware accelerator units controlled by the processor. 
     While the present invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present invention. 
     Additionally, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from its scope. For example, although the invention has been described with a particular emphasis on the AVC encoding standard, the invention can be applied to a video data encoded with a wide variety of standards. 
     Therefore, it is intended that the present invention not be limited to the particular embodiment disclosed, but that the present invention will include all embodiments falling within the scope of the appended claims.

Technology Category: 5