Low Complexity H.264 To VC-1 Transcoder

Abstract

The high definition video adoption has been growing rapidly for the last five years. The H.264 and VC-1 coding standards are two of the recent and dominant coding standards. Compared to H.264, VC-1 is less complex but capable of achieving the same visual quality as H.264. Hence there is increasing importance of techniques which can convert video from H.264 to VC-1 and thereby enable mobile devices to work with less complex codecs. While there has been recent work on VC-1 to H.264 transcoding, the published work on H.264 to VC-1 transcoding is nearly non-existent. This has created the motivation to develop a transcoder that can efficiently transcode a H.264 bitstream into a VC-1 bitstream.A low complex H.264 to VC-1 transcoder is proposed and developed in this research. The proposed architecture is similar to the cascaded transcoder architecture but with important changes. It consists of a complexity reduction module which is the key in this research. The aim of the complexity reduction module is to completely by-pass the motion estimation process, the mode decision process and also the transform size selection process. This is achieved by firstly extracting re-usable data from the incoming H.264 bitstream. Secondly, efficient re-use of mode decisions, macroblock partition size and motion vector are employed. The proposed transcoder was implemented in C programming language and was tested with video sequences at various bit rates and motion activity. The proposed transcoder's performance is comparable to the reference cascaded transcoder in subjective quality and is about 80% faster. This translates to memory and power savings in mobile devices which is the ultimate aim of this research.