[opendtv] Re: A/72 goodies
- From: "John Willkie" <johnwillkie@xxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 17 Sep 2008 14:53:34 -0700
I have to be careful in answering this.
First off, on the list of video frame sizes, I "suspect" that a new one --
perhaps two -- will be introduced in the next month or three.
Also, directly, A/72 does not presage anything about ATSC M/H. A/72 is
about carriage of AVC in MPEG-2 transport streams. At some point, the
companion document about carriage of VC-1 in MPEG-2 transport streams
(candidate standard issued years ago) might also become a standard.
ATSC M/H will have effectively nothing to do with MPEG-2 transport streams.
While M/H will be carried in MPEG-2 transport streams, it will "probably" be
carried in such a way that (by itself) no existing or future MPEG-2
compliant receiver will be able to make any use of it. Not by intent, but
as a direct consequence of several well-considered decisions, including, but
not limited to backwards-compliance. Remember, the purpose is to create
something more robust than 8-VSB, while using 8-VSB as transport. A not so
trival problem space.
I know you like to play that violin -- watching ATSC M/H services on your
existing tv -- for some time, but it simply cannot and will not happen.
Even if you could, you would not be happy with the quality, since the
purpose of M/H is to serve small screens, not large ones, and the output is
tuned to small screens.
I "suspect" that A/72 will be a normative reference in "the new document(s)"
but we'll have to see just what that means in practice.
John Willkie
-----Mensaje original-----
De: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] En
nombre de Manfredi, Albert E
Enviado el: Wednesday, September 17, 2008 12:41 PM
Para: opendtv@xxxxxxxxxxxxx
Asunto: [opendtv] A/72 goodies
What used to be called Table 3, I think, which is actually Table 6.2 of
ATSC A/53, has caused much displeasure over the years, for not allowing
enough frame formats.
Well, with H.264 all of this has changed. Check out Table 6.3 of the new
A/72 standard. It adds:
25 Hz and 50 Hz frame/field rates,
and frame formats
176 X 120
352 X 240
352 X 480
528 X 480
544 X 480
720 X 480
1440 X 1080
over and above what A/53 already lists.
704 and 720 horizontal can optionally be used for 4:3 or 16:9 aspect
ratios. But formats less than 704 horizontal are always 4:3, and greater
than 720 horizontal are always 16:9.
But even more exciting, among these choices is now 1080 at 50p and 1080
at 60p. Wow.
So, does anyone really think that AVC in ATSC is only slated for use
with the M/H standard?
Bert
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