# On requantization in intra-frame video transcoding with different transform block sizes

## Publication Details

Abstract

Transcoding is a technique to convert one video bit-stream into another. While homogeneous transcoding is done at the same coding standard, inhomogeneous transcoding converts from one standard format to another standard. Inhomogeneous transcoding between MPEG-2, MPEG-4 or H.263 was performed using the same transform. With the standardisation of H.264 also a new transform basis and different block size was defined. For requantization from block size 8 × 8 to 4 × 4 this leads to the effect that the quantization error of one coefficient in a block of size 8 × 8 is distributed over multiple coefficients in blocks of size 4 × 4. In our work, we analyze the requantization process for inhomogeneous transcoding with different transforms. The deduced equations result in an expression for the correlation of the error contributions from the coefficients of block size 8 x 8 at each coefficient of block size 4×4. We then compare the mathematical analysis to simulations on real sequences. The reference to the requantization process is the direct quantization of the undistorted signal. It will be shown that the loss is as high as 3 dB PSNR at equivalent step size for input and output bitstream. Also an equation for the choice of the second quantization step size in dependency of the requantization loss is deduced. The model is then extended from the DCT to the integer-based transform as defined in H.264.

FAU Authors / FAU Editors

How to cite

APA: | Bialkowski, J., Barkowsky, M., & Kaup, A. (2005). On requantization in intra-frame video transcoding with different transform block sizes. In Proceedings of the 2005 IEEE 7th Workshop on Multimedia Signal Processing, MMSP 2005 (pp. 549-552). Shanghai. |

MLA: | Bialkowski, Jens, Marcus Barkowsky, and André Kaup. "On requantization in intra-frame video transcoding with different transform block sizes." Proceedings of the 2005 IEEE 7th Workshop on Multimedia Signal Processing, MMSP 2005, Shanghai 2005. 549-552. |

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