[5] I. E. G. Richardson, “H.264 and MPEG-4 Video Compression: Video Coding for Next Generation Multimedia”, Wiley 2nd edition, August 2010.[6] Wikipedia, It is a free, web-based, collaborative, multilingual encyclopedia project supported by the non-profit Wikimedia Foundation.[11] C.C. Cheng, “Fast three step intra prediction algorithm for 4×4 blocks in H.264”, Circuits and Systems, ISCAS, IEEE International Symposium, Vol.2, pp. 1509 – 1512, May 2005.[12] M. Jafani and S. Kasaei, “Fast Intra-Prediction Mode Decision in H.264 Advanced Video Coding”, IEEE Communication Systems, Singapore International Conference ,pp. 1-6, Oct. 2006.[13] M. Roitzsch and M. Pohlack, “Principles for the Prediction of Video Decoding Times Applied to MPEG-1/2 and MPEG-4 Part 2 Video”, Real-Time Systems Symposium, RTSS, 27TH IEEE International, pp. 271 – 280, Dec. 2006.TUSHAR SAXENA FALL 2011THESIS PROPOSALReducing the encoding time of H.264 Baseline profileusing parallel programming techniques INSTRUCTOR: DR. K. R. RAOTushar SaxenaDepartment of Electrical EngineeringUniversity of Texas at ArlingtonEmail: [email protected] 1LIST OF ACRONYMSASO Arbitrary slice orderingAPI Application Programming InterfaceBMA Block-matching algorithmCPU Central Processing UnitCUDA Compute Unified Device Architecture EE Electrical EngineeringFMO Flexible Macro block OrderingGPU Graphical Processing UnitHD High Definition ME Motion EstimationM.S. Master of ScienceNAL Network Abstraction Layer OpenMP Open Multi ProcessingUTA University of Texas at ArlingtonPage 2Reducing the encoding time of H.264 Baseline profileusing parallel programming techniques Abstract: H.264 [5] is a standard for video compression for recording, compression and distribution of high definition video. It is also designed for multiview coding, scalable coding, etc. Baselines and extended profiles are designed for handheld devices, video streaming, etc. It basically reduces the amount of information required to reproduce the input video by exploiting redundancy in the pictures it is encoding, both spatially (within the same picture) and temporally (between pictures). But these computations are very complex. It increases the encoding time so as to restrictits use for real time applications. To make it suitable for real-time applications, the encoding time of H.264 video codec should be reduced. This can be achieved by encoding video frames parallely instead of sequentially. Hence more than one video frame [depending on the number of cores on the system] will be encoded in the same time duration of a single video frame. With the advancement in technology and the need for more bandwidth and processing power increasing on a daily basis, many parallel programming techniques [10] are now available. Since the scope of this thesis is to reduce the encoding time in H.264 Baselineprofile only on central processing units (CPU), a set of libraries known as Open Multi Processing (OpenMP) will be used for this purpose.What is H.264:H.264 [5] is a video compression standard which can achieve high quality video in relatively low bitrates. It can mainly achieve this because of its very strong salient featurei.e. Variable block-size motion compensation with small block sizes [See Fig.1]Fig.1: Block sizes available for motion prediction in H.264 [2]The encoder [see fig. 2] splits the input video signal into macro blocks of 16x16 pixels. The macro blocks are then encoded by a technique known as motion estimation (ME) [1], an essential part in inter-picture prediction, makes a great contribution to reduce the bit rate.Page 3FIG.2: H.264 VIDEO ENCODER BLOCK DIAGRAM [2]Once the encoding of a frame is done, the coded video data is organized into network abstraction layer (NAL) units [see fig. 3], each of which is effectively a packet that contains an integer number of bytes. The first byte of each NAL unit is a header byte thatcontains an indication of the type of data in the NAL unit and the remaining bytes containpayload data of the type indicated by the header. FIG.3: NAL unit interface between encoder and decoder [2]The NAL units are then made available at the input of the decoder [see fig. 4] where theencoded data is decoded to obtain the original frame.FIG.4: H.264 VIDEO DECODER BLOCK DIAGRAM [2]Page 4ME [see fig. 5] is an important part of inter-picture prediction. It is a process of determining the best motion vectors that describe the transformation from one frame to another. MV described as (dx, dy) is displacement vector of a moving object. An algorithm known as block-matching algorithm (BMA) [3] is used in H.264 standard to locate matching macro block in a frame based on the position of this macro block in reference frame. FIG.5: Multi frame ME [4]H.264 exploits both spatial redundancy as well as temporal redundancy. Temporal redundancy is exploited using ME [see fig. 5] whereas spatial redundancy is exploited using the prediction modes [see fig. 6]. Since these computations are very complex, it increases the encoding time drastically restricting the use of H.264 for real time application. For homogeneous regions the macro block sizes are 16x16 with four intra prediction modes [see fig. 7] but for non homogeneous regions the block sizes are 4x4 with nine prediction modes [see fig. 6]. Fig.6: Nine intra prediction modes for 4x4 block sizes [11]Page 5FIG.7: Four intra prediction modes for 16x16 block sizes [12]Profiles of H.264:FIG.8: Profiles of H.264 [5]The four profiles [see fig.8] of H.264: Baseline, Main, Extended and High. 1] Baseline Profile: It is primarily for low-cost applications that require additional data loss robustness, this profile is used in some videoconferencing and mobile applications. This profile includes all features that are supported in the Constrained Baseline Profile, plus three additional features that can be used for loss robustness (or for other purposessuch as low-delay multi-point video stream compositing). 2] Main Profile: It is designed for digital storage media and television broadcasting. H.264 main profile which is the subset of high profile was designed with compression coding efficiency as its main target.
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