  A transcoding scheme for the High Efficiency Video Coding (HEVC) is proposed
that allows any partial frame modification to be followed by a partial
re-compression of only the modified areas, while guaranteeing identical
reconstruction of non-modified areas. To this end, first, syntax elements of
all Coding Units (CU) in the frame are parsed and decoded according to their
scan order. Then CUs that are collocated with a replaced area are re-encoded
with new content to generate a partial set of new syntax elements. In order to
avoid spatial propagation of the decoding mismatch due to the new content, CUs
on the border of the replaced area are losslessly coded such that
reconstruction of immediately neighboring CUs in the scan order are protected
from the modification. The proposed method has been implemented on top of the
HEVC test Model (HM) in All-Intra (AI) coding configuration and experiments
show that, depending on the test parameters, it can offer both a bitrate saving
(up to 4% in terms of BD-BR) and a transcoding acceleration (up to 83%)
compared to a full transcoding scheme.
