A frame type for a current SBR frame is determined according to a type of
end border of a previous frame, as well as presence of a transient in the
current SBR frame. A start border is determined according to the end
border of the previous SBR frame. For a FIXFIX frame, a low
time-resolution setting is used. For a FIXVAR or a VARVAR frame, a search
for intermediate borders is conducted in the region between the transient
and maximum allowed end border location. The end border is also
determined at this stage. If there is excess capacity for more borders,
another search is conducted in the region between the transient and the
start border. For a VARFIX frame, only one search needs to be conducted,
in the whole region partitioned by a variable start border and a fixed
end border. All of the above are accomplished with two Forward Search
operations and one Backward Search operation. They employ the same
principle, which is based on evaluating the signal variation of a time
segment, but with minor variations to suit the scenarios in which they
are applied.