  The ability to efficiently switch from one pre-encoded video stream to
another (e.g., for bitrate adaptation or view switching) is important for many
interactive streaming applications. Recently, stream-switching mechanisms based
on distributed source coding (DSC) have been proposed. In order to reduce the
overall transmission rate, these approaches provide a "merge" mechanism, where
information is sent to the decoder such that the exact same frame can be
reconstructed given that any one of a known set of side information (SI) frames
is available at the decoder (e.g., each SI frame may correspond to a different
stream from which we are switching). However, the use of bit-plane coding and
channel coding in many DSC approaches leads to complex coding and decoding. In
this paper, we propose an alternative approach for merging multiple SI frames,
using a piecewise constant (PWC) function as the merge operator. In our
approach, for each block to be reconstructed, a series of parameters of these
PWC merge functions are transmitted in order to guarantee identical
reconstruction given the known side information blocks. We consider two
different scenarios. In the first case, a target frame is first given, and then
merge parameters are chosen so that this frame can be reconstructed exactly at
the decoder. In contrast, in the second scenario, the reconstructed frame and
merge parameters are jointly optimized to meet a rate-distortion criteria.
Experiments show that for both scenarios, our proposed merge techniques can
outperform both a recent approach based on DSC and the SP-frame approach in
H.264, in terms of compression efficiency and decoder complexity.
