Transcoding and Optimization of H.264
Date Issued
2005-07-31
Date
2005-07-31
Author(s)
DOI
932213E002137
Abstract
A key objective of this project is to develop a transcoder for converting an MPEG-2 video bitstream to
the H.264 format. Along with the conversion, we also reduce the image resolution by half in each dimension.
For computational efficiency, we avoid full decompression and full recompression in the spatial domain. The
output bitstream is fully compliant to the H.264 standard. In our technique, the "transform conversion"
between the DCT of MPEG-2 and the modified DCT of H.264 is incorporated in the down-sampling process.
Inter and intra frames are processed separately. For transcoding of intra frames, both DCT-to-PEL and
DCT-to-DCT architectures are considered, while for inter frames a DCT-to-DCT architecture is adopted.
Another objective of this project is to improve the computational efficiency of two core modules, motion
estimation and mode decision, of H.264. For motion estimation, we develop a fast algorithm with adaptive
search strategy and intelligent reference frame selection. Compared with the H.264 reference software JM
8.5, this algorithm achieves, on the average, a 600% reduction of encoding time. For mode decision, we
exploit the correlation between neighboring image blocks to predict the best possible mode. Compared with
the reference software, this method achieves about 204% reduction of encoding time with negligible PSNR
drop and bit rate increase. Integrating these two fast algorithms in the H.264 reference software, this
combined method, on the average, is about 12.1 times faster in the total encoding time, at the cost of a slight
PSNR drop.
Subjects
vH.264
DCT
transcoding
down-sampling
variable block-size
motion
estimation
estimation
mode decision
multiple reference frames
Publisher
臺北市：國立臺灣大學電信工程學研究所
Type
report
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