Image Processing Reference
In-Depth Information
11
The MPEG-2 Codec
11.1
Extending the Range of Capabilities
The MPEG-2 codec is credited with making the digital television and DVD industries pos-
sible. Certainly these were not feasible with MPEG-1. The coding support has been
enhanced to include MPEG-2 HD for high-definition TV applications. The profiles and
levels supported by MPEG-2 are summarized in Appendix F.
MPEG-2 is designed to run on a much wider variety of networks and carriage mech-
anisms than MPEG-1. MPEG-1 was designed to run in error-free environments such as
CD-ROMs.
Although MPEG-1 was successful when it was deployed, it did not deliver all the
requirements for broadcasting a TV service. To be fair, it was not designed to do that since
it was intended as a delivery format for low bit-rate content for modems and CD-ROM
disks.
MPEG-2 builds on MPEG-1 by adding some extra capabilities to the encoding
process. Fundamentally, it works the same way but the enhancements produce better
quality, larger picture sizes, and additional support for interlacing and film-to-TV transfer.
11.2
Interlace Tools
While the technical reasons for implementing interlaced video are largely eliminated
when dealing with digital video and progressively scanned displays, there are still some
technical experts that argue that interlaced video presents a smoother motion representa-
tion than progressively scanned content.
The MPEG-2 standard introduces some additional tools to cope with the coding of
interlaced material. In particular, some variants of the I-, P-, and B-frames provide a means
of coding individual fields. These I-fields, P-fields and B-fields are much like frames.
Maintaining the correct ordering of them as odd and even fields is very important.
The correct sequencing of the fields as either odd or even lines in the picture and
their temporal placement as first or second in the pair of fields that make a frame is
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