Visual Media Coding and Transmission

5.8 A Robust FMO Scheme for H.264/AVC Video Transcoding

5.8.1 Problem Definition and Objectives

As explained in Section 5.2, the H.264/AVC standard [56] includes several error-resilience tools, whose proper use and optimization is left open to the codec designer. In the work described here, focus is on studying adaptive FMO schemes to enhance the robustness of pre-encoded video material.

5.8.2 Proposed Technical Solution

According to the H.264/AVC syntax, each frame is partitioned into one or more slices, and each slice contains a variable number of MBs. FMO is a coding tool supported by the standard that enables arbitrary assignment of each MB to the desired slice. FMO can be efficiently combined with FEC-based channel coding to provide unequal error protection (UEP). The basic idea is that the most important slice(s) can be assigned a stronger error-correcting code.

The goal is to design efficient algorithms that can be used to provide a ranking of the MBs within a frame. The ranking order is determined by the error induced by the loss of the MB at the decoder side. In other words, those MBs that, if lost, cause a large increase of distortion should be given higher protection. The total increase of distortion, measured in terms of MSE, can be factored out as follows:

where t is the frame index and i the MB index, and:

• D_MV (t,i) is the additional distortion due to the fact that ...