[opendtv] Re: Why can't POSTAGE STAMPS be Eliminated???
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 19 May 2006 08:04:35 -0400
At 7:17 PM -0700 5/18/06, Kilroy Hughes wrote:
>Regular MPEG-2 decoder chips, cores, and software handle 720x480 11/10 =
>Sample Aspect Ratio "pixels" for 4:3 as well as the 16:9 anamorphic (75% =
>squeezed) version, and other non "NTSC" sample sizes ("half D1", etc.) =
>commonly used for cable, satellite, DVD-V, etc.; all of which are =
>included in the MPEG spec.
>
>It probably isn't cost effective to build special "retarded" MPEG-2 =
>decoder chips with broken functionality in memory of Table 3. =20
>
>But you never know. Some manufacturers may have gone to great trouble =
>to rig their sets to blow up on legal MPEG image formats they considered =
>subversive.
We've been down this path before, as Mark will attest to.
The world is filled with non-conformant MPEG-2 chips. Mark worked
unsuccessfully to get the ATSC to allow a simple addition to Table 3
- i.e. 720 x 480 in both pixel aspect ratios. For those who may not
be aware, Table 3 only allows 704 x 480 formats. This simple, MPEG-2
conformant change was vetoed in the ATSC because some early decoder
implementations were "hard wired" to Table 3.
Kilroy may also be aware - I think he participated in some of the
meetings - about the effort to use a reserved bit, to signal
information about incorrect 3:2 pulldown sequences in an MPEG-2 bit
stream. This was shut down at ISO-MPEG by the Japanese delegation
(and possibly others) because some manufacturers had hard coded
around some reserved bits in early decoder implementations - It was
feared that these decoders would break if the reserved bits were used.
Bottom line, the MPEG-2 spec is frozen because of non-conformant
implementations.
Regards
Craig
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