Study and Comparison of MPEG 2 and H 264 main profiles and available transcoding methods EE 5359 Priyanka Ankolekar 1000 51 4497 Introduction Development of international video coding standards like MPEG 2 led to a boost in multimedia applications like digital video recording and teleconferencing On growing demand for better compression performance led to advanced video coding standards like H 264 H 264 is superficially similar to MPEG 2 However there are significant differences in the details This project aims to compare the MPEG 2 and H 264 main profiles and to discuss related transcoding methods MPEG 2 Second of several standards developed by the moving pictures experts group 16 Used as the format of digital TV signals and direct broadcast satellite TV systems MPEG 2 is not optimized for low bit rates like 1Mbps But it outperforms MPEG 1 at 3Mbps and above It is used for higher data rates of 4Mbps DVD and 19Mbps HDTV MPEG 2 devices are back compatible with MPEG 1 MPEG 2 Video is formally known as ISO IEC 13818 2 and as ITU T Rec H 262 21 MPEG 2 Profiles A profile is a collection of compression tools that together make up the coding system A different profile means that a different set of compression tools is available 22 There are five profiles in MPEG 2 as summarized below MPEG 2 Profiles 16 Abbr Name Picture Coding Types Chroma Format Aspect Ratios Scalable modes SP Simple profile I P 4 2 0 square pixels 4 3 or 16 9 none MP Main profile I P B 4 2 0 square pixels 4 3 or 16 9 none SNR SNR Scalable profile I P B 4 2 0 square pixels 4 3 or 16 9 SNR signal to noise ratio scalable Spatial Spatially Scalable profile I P B 4 2 0 square pixels 4 3 or 16 9 SNR or spatial scalable High profile I P B 4 2 2 or 4 2 0 square pixels 4 3 or 16 9 SNR or spatial scalable HP MPEG 2 Encoder 10 MPEG 2 Encoder contd DCT 2 dimensional 8x8 for intra frames 8x8 pels for inter frames 8x8 residual blocks Quantizer Quantizes DCT coefficients using a default or modified matrix 8 16 19 22 26 27 29 34 16 16 22 24 27 29 34 37 19 22 26 27 29 34 34 38 22 22 26 27 29 34 37 40 22 26 27 29 32 35 40 48 26 27 29 32 35 40 48 58 26 27 29 34 38 46 56 69 27 29 35 38 46 56 69 83 Motion Estimation and Compensation In the motion estimation process motion vectors for predicted and interpolated pictures are coded differentially between macroblocks For the motion compensation process integer and half pel resolution motion vectors are used to predict from previously decoded pictures MPEG 2 Decoder 7 H 264 Developed by the Joint Video Team JVT Achieves MPEG 2 quality compression at almost half the bit rate 7 Significant coding efficiency simple syntax specifications and seamless integration of video coding into all current protocols and multiplex architectures Supports various applications such as video broadcasting video streaming and video conferencing over fixed and wireless networks and over different transport protocols 4 H 264 Profiles Comparison 11 Each H 264 profile specifies a subset of entire bitstream of syntax and limits that shall be supported by all decoders conforming to that profile There are three profiles in the first version Baseline Main and Extended There are four High profiles defined in the fidelity range extensions 19 Baseline Extended Main High I and P Slices Yes Yes Yes Yes B Slices No Yes Yes Yes SI and SP Slices No Yes No No Multiple Reference Frames Yes Yes Yes Yes In Loop Deblocking Filter Yes Yes Yes Yes CAVLC Entropy Coding Yes Yes Yes Yes CABAC Entropy Coding No No Yes Yes Flexible Macroblock Ordering FMO Yes Yes No No Arbitrary Slice Ordering ASO Yes Yes No No Redundant Slices RS Yes Yes No No H 264 Profiles Coding parts 1 H 264 Encoder 9 H 264 Encoder 4x4 integer DCT Smaller blocksize leads to a significant reduction in ringing artifacts Quantization and scan H 264 standard specifies the math formula for the quantization process Deblocking filter To reduce the blocking artifacts in the block boundaries and to stop the propagation of accumulated coded noise The filtered image is used in motion compensated prediction of future frames and helps achieve more compression Intra prediction The encoder derives a predicted block based on its prediction with previously decoded samples for I frames Inter prediction Performed on the basis of temporal correlation and consists of motion estimation and motion compensation Motion vector resolution is pel Supports large number of block sizes Multiple reference pictures upto 32 previously coded frames H 264 Decoder 7 Comparison between H 264 and MPEG 2 Algorithm Characteristic MPEG 2 H 264 General Motion compensated predictive residual transformed entropy coded Same basic structure as MPEG Block size 8x8 Macroblock size 16x16 frame mode 16x8 field mode 16x16 Intra Prediction None Multi direction Multi pattern Quantization Scalar quantization with step size of constant increment Scalar quantization with step size of increase at the rate of 12 5 Entropy coding VLC CAVLC CABAC Weighted prediction No Yes 16x16 8x16 16x8 8x8 4x8 8x4 4x4 Comparison between H 264 and MPEG 2 contd Algorithm Characteristic MPEG 2 H 264 Reference picture One picture Multiple pictures Motion Estimation Blocks 16x16 16x16 8x8 8x4 4x4 Entropy Coding Multiple VLC Tables Arithmetic Coding and adaptive VLC Tables Frame Distance for Prediction 1 Unlimited forward backward Fractional Motion Estimation 1 2 Pixel MPEG2 1 4 Pixel Deblocking Filter None Dynamic edge filters Scalable coding support 2 Yes layered picture spatial SNR temporal scalability With some support on temporal and SNR scalability Bit rates with same quality HD video with resolution 1920 x 1080 12 20 Mbps 7 8 Mbps Transmission rate 2 15 Mbps 64 kbps 150 Mbps Performance comparison between H 264 and MPEG 2 Simulations Test streams used Foreman CIF News CIF Carphone QCIF 26 Codecs used MPEG 2 25 and H 264 24 Profiles for which the simulations were run Main and Simple Baseline Compression ratio Original file size Compressed file size Formula to compute PSNR for MPEG 2 MAXI 255 Performance comparison between H 264 and MPEG 2 Simulation Foreman MPEG 2 Main Profile H 264 Main Profile Performance comparison between H 264 and MPEG 2 Simulation results Foreman Parameter MPEG 2 H 264 Input video resolution 352 x CIF fps 30 30 frames encoded 90 90 GOP I P B B P B B I B B P B B P PSNR Y dB 30 42 37 03 PSNR U dB 39 1 41 08 PSNR V dB 39 6 43 81 Bit rate kbits second 481 00 481 06 Original file size yuv MB 13 3 13 3 Compressed file size KB
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