DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

422P@ML allows 608 lines at
25 Hz frame rate, but is limited
to 512 lines at 29.97 and 30 Hz
frame rates.
SMPTE 308M, Television – MPEG-2
4:2:2 Profile at High Level.
Every compliant MPEG-2 decoder must be capable of
decoding an MPEG-1 constrained-parameters bitstream
(CPB). I include MPEG-1 CPB at the lower left of
Table 40.1, as if it were both a profile and a level, to
emphasize this MPEG-2 conformance requirement.
The simple profile has no B-pictures. Prohibition of
B-pictures minimizes encoding latency, and minimizes
buffer storage at the decoder. However, the simple
profile lacks the compression efficiency of B-pictures.
Of the eight combinations in Table 40.1, only two are
important to television. MP@ML is used for SDTV
distribution, and for DVD, at rates from about 2 Mb/s
to about 6 Mb/s. MP@HL is used for HDTV distribution,
usually at about 20 Mb/s.
The 4:2:2 profile allows 4:2:2 chroma subsampling; it is
intended for use in television production. The major
reason for a separate 4:2:2 profile is that main profile
disallows 4:2:2 chroma subsampling. MPEG-2’s high
profile allows 4:2:2 subsampling, but to require highprofile
conformance obliges a decoder to handle SNR
and spatial scalability. Two combinations in Table 40.1
are relevant to television production: 422P@ML is
expected to see some application in the studio, at
about 50 Mb/s; 422P@HL may be used in HDTV
production. Some numerical parameter limits of main
and 4:2:2 profiles are presented in Table 40.2 opposite.
4:2:2 profile at high level (422P@HL) is defined in
MPEG-2. In addition to MPEG-2’s requirements for
422P@HL, SMPTE 308 imposes these restrictions on
GOP structures permitted at high data rates, as shown
in Table 40.3:
Bit rate Interlace? GOP structure allowed
0 to 175 any any
175 to 230 any
interlaced
230 to 300 { progressive
I-only, IP, or IB
I-only
I-only, IP, or IB
Table 40.3 GOP restrictions in SMPTE 308M
476 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES