Bhumika Makwana 1000 441 934 EE 5359 Multimedia Processing Research Project Proposal Performance analysis of H 264 MPEG4 based of different profiles Submitted By Bhumika Makwana Under the guidance of Dr K R Rao 1 Bhumika Makwana 1000 441 934 Table of Contents 1 2 3 4 5 Background 3 Introduction 3 Technical Details 4 Profiles and Level 7 References 10 Figures 1 2 3 4 5 6 H 264 encoder 4 Diagram depicting how the loop filter works on the edges of the blocks and sub blocks 5 Intra prediction 4x4 6 H 264 decoder 7 The specific coding parts of the Profiles in H 264 8 A typical sequence with I B and P frames 9 2 Bhumika Makwana 1000 441 934 Background The number of devices using multimedia application is getting bigger day by day End users constantly demand for rich multimedia content For instance user demanding for broadcast TV channel on mobile handset user playing games online or surfing the web user constantly checking stock exchange etc To meet this exponentially increasing demand for rich and high definition multimedia contents there is a need for advance codecs which must be capable of providing below features Less network bandwidth Less storage space especially for video files Higher video quality for a given bitrates High resolution Less complexes Easy to implement One can find video compression technology in great diversity of products and services just because of its own advances in past 2 decades From mp3 players to Blue Ray players compressed video is now an indispensible part of our daily life The new H 264 AVC standard is at the forefront of this technology H 264 MPEG 4 AVC codec introduction H 264 is an open licensed standard developed by the JVT Joint Video Team that supports the most efficient video compression techniques available today Without compromising image quality an H 264 encoder can reduce the size of a digital video file by more than 80 compared with the Motion JPEG format and as much as 50 more than with the MPEG 4 Part 2 standard This means that much less network bandwidth and storage space are required for a video file Or seen another way much higher video quality can be achieved for a given bit rate 1 2 H 264 standard can deliver high quality video to a variety of devices ranging from low powered cell phones to high powered Blu ray devices because of its flexible bit stream control This has enable the H 264 standard to supersede some of the video compression formats that are commonplace today 3 Bhumika Makwana 1000 441 934 Technical Details Figure 1 H 264 encoder 3 4x4 Integer transform The H 264 employs a 4x4 integer DCT as compared to 8x8 DCT adopted by the previous standards The smaller block size leads to a significant reduction in ringing artifacts Also the 4 x 4 transform has the additional benefit of removing the need for multiplications Quantization and scan The H 264 standard specifies the mathematical formulae of the quantization process The scale factor for each element in each sub block varies as a function of the quantization parameter associated with the macroblock and as a function of the position of the element within the sub block The rate control algorithm controls the value of the quantization parameter Two types of scan pattern are used for 4x4 blocks one for frame coded macroblocks and one for field coded macroblocks 4 Bhumika Makwana 1000 441 934 Context based adaptive variable length coding CAVLC and Context based adaptive binary arithmetic coding CABAC entropy coding H 264 uses different variable length coding methods in order to match a symbol to a code based on the context characteristics They are context based adaptive variable length coding CAVLC and context based adaptive binary arithmetic coding CABAC All syntax elements except for the residual data are encoded by the Exp Golomb codes In order to read the residual data quantized transform coefficients zig zag scan interlaced or alternate scan non interlaced or field is used For coding the residual data a more sophistical method called CAVLC is employed Also CABAC is employed in Main and High profiles CABAC has more coding efficiency but higher complexity compared to CAVLC Deblocking filter H 264 employs a deblocking filter to reduce the blocking artifacts in the block boundaries and stops the propagation of accumulated coded noise The filter is applied after the inverse transform before reconstructing and storing the macroblock for future predictions and in the decoder before reconstructing and displaying the macroblocks The deblocking filter is applied across the edges of the macroblocks and the sub blocks The filtered image is used in motion compensated prediction of future frames and helps achieve more compression Figure 2 Diagram depicting how the loop filter works on the edges of the blocks and sub blocks Intra prediction During intra prediction the encoder derives a predicted block based on its prediction with previously decoded samples The predicted block is then subtracted from the current block and then encoded There are a total of nine prediction modes Figure 3 for each 4x4 luma block four prediction modes for each 16x16 luma block and four modes for each chroma block 5 Bhumika Makwana 1000 441 934 Figure 3 Intra prediction 4x4 5 Inter prediction Inter prediction is performed on the basis of temporal correlation and consists of motion estimation and motion compensation As compared to the previous standards H 264 supports a large number of block sizes from 16x16 to 4x4 Moreover H 264 supports motion vector accuracy of one quarter of the luma sample Reference pictures Unlike the previous standards that just use the immediate previous I or P picture for inter prediction H 264 has the ability to use more than one previous reference picture for inter prediction thus enabling the encoder to search for the best match for the current picture from a wider set of reference pictures than just the previously encoded one 6 Bhumika Makwana 1000 441 934 H 264 Decoder Figure 4 H 264 decoder It includes all the control information such as picture or slice type macroblock types and subtypes reference frames index motion vectors loop filter control quantizer step size etc as well as coded data comprising of quantized transform coefficients The decoder of Figure works similar to the local decoder at the encoder a simplified description is as follows After entropy CABAC or CAVLC decoding the transform coefficients are inverse scanned and inverse quantized prior to being inverse
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