MPEG-2 Nonscalable Coding Modes:
The MPEG-2 algorithm defined in the MAIN Profile is
a straightforward extension of the MPEG-1 coding scheme
to accommodate coding of interlaced video, while retaining
the full range of functionality provided by MPEG-1. Identical
to the MPEG-1 standard, the MPEG-2 coding algorithm
is based on the general Hybrid DCTDPCM coding scheme
as outlined in Fig. 9, incorporating a macroblock structure,
motion compensation and coding modes for conditional
replenishment of macroblocks. The concept of I-pictures,
P-pictures, and B-pictures as introduced in Fig. 10 is fully
retained in MPEG-2 to achieve efficient motion prediction
and to assist random access functionality. Notice that the
algorithm defined with the MPEG-2 SIMPLE Profile is
basically identical with the one in the MAIN Profile, except
that no B-picture prediction modes are allowed at the
encoder. Thus the additional implementation complexity
and the additional frame stores necessary for the decoding
of B-pictures are not required for MPEG-2 decoders only
conforming to the SIMPLE Profile.
Field and Frame Pictures: MPEG-2 has introduced the
concept of frame pictures and field pictures along with
particular frame prediction and field prediction modes to
accommodate coding of progressive and interlaced video.
For interlaced sequences it is assumed that the coder input