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What is Transcoding The operation of converting video in one format to another format. It is the ability to take existing video content and change the bitrate and/or resolution in order to view it on another video playback device

Need for Transcoding MPEG-2 [4] has been a widely accepted video coding standard for various applications ranging from DVD to digital tv. broadcast. The most important goal of MPEG-2 was to make the storage and transmission of digital AV material more efficient. However new H.264 AVC standard [13] has an even broader perspective to support high and low bit-rate multimedia applications on existing and future networks.

Need for TranscodingContd… H.264 requires half of the space to store video content when compared to MPEG-2[1]. Hence there is need to find compatibility between MPEG- 2 and H.264 devices.

MPEG-2 Encoder/Decoder Fig.1 MPEG-2 encoder/decoder [1]

H.264 Encoder Fig.2 H.264 Encoder [9].

Different MacroBlock sizes of H.264 for Motion Estimation Fig.3 Different macroblocks in H.264[ 8].

Normal Method of motion estimation In H.264, inter frame motion estimation is performed using different MB sizes from 16 × 16 to 4 × 4 [8]. For each MB, all different sizes are evaluated and the one leading to the minimum rate-distortion (RD) cost is then selected. This guarantees the optimal block size for the final encoding but at the expense of a high-computational cost.

How is this transcoder Different? Machine learning tools are used to exploit the correlation between the macroblock(MB) [1] decision of the H.264 video format and the distribution of the motion compensated residual in MPEG-2. Dynamic motion window technique is also proposed to further speed-up the decision process.

The Algorithm for motion estimation for proposed trancoder The proposed MPEG-2 to H.264 transcoder consists of two parts: an MPEG-2 decoder followed by an H.264 encoder. First, the transcoder fully decodes the MPEG-2 sequence, and the information required by the decision trees and the dynamic motion window mechanism is gathered during this stage. The information is given as input to decision tree. The H.264MB mode decision is replaced by a simple mode assignment.

FAST MB MODE DECISION USING MACHINE LEARNING Creating the Training Files Fig.4 Training algorithm for decision tree[2].

Decision Trees Fig. 5 Decision tree for deciding the macro block mode of H.264 encoder [1].

Dynamic motion window Adapting the search range based on the motion vector of the incoming MB could reduce the motion estimation[1]. Dynamic motion window is combination of two methods. Dynamic search range based on the length of the motion vectors in the MPEG-2 video [2]. Orientation of the Motion vectors [2].

Conclusions Computational complexity of Inter prediction Motion estimation of H.264 encoder of transcoder can be reduced by 90% [1]. Machine learning tool is Weka J4.8 [3]. Software used is JM reference software version 17.2 [8]. MPEG- 2V12 reference software for MPEG- 2 [6].

References 1. H. Kalva,et al,”An MPEG-2 to H.264 video transcoder in the baseline profile.”IEEE Transactions on circuits and systems for video technology,vol-20,no-5,pp , May G. Fernández-Escribano, et al, “Reducing motion estimation complexity in MPEG-2 to H.264 transcoding,” in Proc. IEEE International Conference Multimedia Expo (ICME), Beijing, China, pp. 440–443,Jul. 2–5, I. E. G. Richardson, “H.264/MPEG-4, part 10,” in H.264 and MPEG-4Video Compression, Hoboken, NJ: Wiley, pp. 159–223, G. Fernández-Escribano, et al, “A fast MB mode decision algorithm for MPEG-2 toH.264 P-frame transcoding,” IEEE Transactions on circuits and systems for video technology,vol. 18, no. 2, pp. 172–185, Feb JM software -http ://iphome.hhi.de/suehring/tml/. 6. MPEG-2 software- 7. M. Isnardi,”MPEG-2 video compression“ Sarnoff corporation,Nov 29, W. W. Cohen and Y. Singer, “A simple, fast, and effective rule learner,” in Proc. 16th Natl. Conf. Artificial Intelligence, Orlando, FL, pp. 335–342, Jul. 18–22, T. Wiegand,and Gary J. Sullivan, “Overview of H.264/AVC video coding standards,” IEEE Transactions on circuits and systems for video technology, vol. 13, no. 7,pp July 2003.