Information Technology Reference
In-Depth Information
Figure 5.46:
An MPEG-4 object-based decoder is essentially a multi-layered compositing device, using keying to
give the illusion that objects are in front of a background.
Figure 5.47 shows that MPEG-4 codes each arbitrarily shaped video object by creating a
bounding rectangle
within
which the object resides. The shape and the texture of each video object are re-created at the decoder by two
distinct but interrelated processes. The bounding rectangle exists on macroblock boundaries and can change from
VOP to VOP. At each VOP, the bitstream contains horizontal and vertical references specifying the position of the
top-left corner of the bounding rectangle and its width and height.
