TUSHAR SAXENA FALL 2011 THESIS PROPOSAL Reducing the encoding time of H 264 Baseline profile using parallel programming techniques INSTRUCTOR DR K R RAO Tushar Saxena Department of Electrical Engineering University of Texas at Arlington Email tushar saxena mavs uta edu Page 1 LIST OF ACRONYMS ASO Arbitrary slice ordering API Application Programming Interface BMA Block matching algorithm CPU Central Processing Unit CUDA Compute Unified Device Architecture EE Electrical Engineering FMO Flexible Macro block Ordering GPU Graphical Processing Unit HD High Definition ME Motion Estimation M S Master of Science NAL Network Abstraction Layer OpenMP Open Multi Processing UTA University of Texas at Arlington Page 2 Reducing the encoding time of H 264 Baseline profile using 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 restrict its 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 Baseline profile 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 feature i 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 3 FIG 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 that contains an indication of the type of data in the NAL unit and the remaining bytes contain payload 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 the encoded data is decoded to obtain the original frame FIG 4 H 264 VIDEO DECODER BLOCK DIAGRAM 2 Page 4 ME 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 5 FIG 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 purposes such 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 3 Extended Profile Extended profile intended as the streaming video profile this profile has relatively high compression capability and some extra tricks for robustness to data losses and server stream switching 4 High Profile High profile powers more visual communication with fewer resources thus limiting or avoiding costly network upgrades High definition HD systems benefit the most from this profile and this new technology will accelerate the adoption of HD communication across organizations Page 6 Advantages and Disadvantage of H 264 H 264 encoding and decoding is more computationally complex than some other codecs such as MPEG 4 Part 2 13 This is mainly because of the variable block size motion compensation technique adopted with small block sizes and adaptive intra directional predictions This limits its use for real time applications However the compression performance of H 264 is significantly better than these so it depends on the requirement of the application Changes adopted in H 264 Baseline profile video codec to reduce the encoding time The only way to make H 264 suitable for real time applications is to reduce the encoding time This can be achieved by encoding many frames parallely From the software point of view this can be done by
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