[opendtv] Re: BBC Demonstrates HDTV Broadcasts over SD Channels
- From: "John Willkie" <JohnWillkie@xxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 22 Jun 2005 21:18:38 -0700
Actually, Tom, we've been through this two separate times before, in two
different years. The first time was almost exactly two years ago. Sort of
sad that you didn't learn.
MPEG-2 places no constraint on which of the three pixel sizes you use with a
video frame of a particular size. ATSC, however, does place such a
constraint. If you look at A/53c, section 5.1.2, and table A3 (which
follows that section heading) you can see that 480x640 can have square
pixels or 9/16 sized pixels; 480x704 can have 3/4 or 9/16 sized pixels.
But, John was talking about display aspect ratios, not sample aspect ratios.
I forgot to do another calculation to refute what he said, in the context of
480x640. If one divides 480 by three, one gets 160. If one multiplies 160
x 4, one gets 640. I'm still looking for a 480 line video format with a
16:9 display aspect ratio.
This "as specified separately in the stream" must be another one of your
non-sequiturs; any such type of description is optional -- and was the
subject of much discussion today on my PSIP list
(EtherGuideCallsign-request@xxxxxxxxxx) by persons more knowledgeable than
myself -- and is seldom seen. Other than the active format description and
bar data -- which actually doesn't handle what you are alleging -- just
where is this separately defined stream data found?
Have you ever written a transport stream parser or analyzer, Tom? I have.
It's called EtherGuide Ferret.
John Willkie
----- Original Message -----
From: "Tom Barry" <trbarry@xxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Wednesday, June 22, 2005 7:59 PM
Subject: [opendtv] Re: BBC Demonstrates HDTV Broadcasts over SD Channels
> I think we have had this discussion on this list before. So keep
> in mind that the 480 line resolutions are not square pixels. That
> is, the display resolution ratio will not be the same as the
> ratio of horizontal to vertical encoded pixels.
>
> With 480 line SDTV it will likely be coded as 704x480 or 640x480
> but will still be displayed (as specified separately in the
> stream) as either a 16:9 or 4:3 picture. This is true even though
> it is obvious that 704/480 does not equal either of those ratios.
>
> - Tom
>
>
> John Willkie wrote:
>
> > John;
> >
> > All my specs are on another computer. I will refer to them in short
order.
> > However, by dividing 480 by 9, one gets 53.3. Multiplying 53.3 x 16 one
> > gets 853.33. Kinda funny to call that a display aspect ratio of 16x9,
isn't
> > it? I need to refer to 13818-1 before I address the sample aspect
ratio.
> >
> > John Willkie
> > ----- Original Message -----
> > From: "John Shutt" <shuttj@xxxxxxxxx>
> > To: <opendtv@xxxxxxxxxxxxx>
> > Sent: Wednesday, June 22, 2005 5:23 PM
> > Subject: [opendtv] Re: BBC Demonstrates HDTV Broadcasts over SD Channels
> >
> >
> >
> >>John,
> >>
> >>What do you mean by this? 704x480 can be 4x3 or 16x9. Only the aspect
> >>ratio of the pixel changes, so in theory 704x480 can be exactly any
aspect
> >>ratio.
> >>
> >>John
> >>----- Original Message -----
> >>From: "John Willkie" <JohnWillkie@xxxxxxxxxxxxx>
> >>
> >>>sure, the specs permit it. But, in the real world, it's kinda hard.
> >
> > Oh,
> >
> >>>and 480 x 704, by my calculation isn't 16x9, although it's close.
> >>>
> >>>John Willkie
> >>
> >>
> >>
> >>
> >>----------------------------------------------------------------------
> >>You can UNSUBSCRIBE from the OpenDTV list in two ways:
> >>
> >>- Using the UNSUBSCRIBE command in your user configuration settings at
> >
> > FreeLists.org
> >
> >>- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
> >
> > unsubscribe in the subject line.
> >
> >
> >
> >
> > ----------------------------------------------------------------------
> > You can UNSUBSCRIBE from the OpenDTV list in two ways:
> >
> > - Using the UNSUBSCRIBE command in your user configuration settings at
FreeLists.org
> >
> > - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
unsubscribe in the subject line.
> >
> >
>
>
> ----------------------------------------------------------------------
> You can UNSUBSCRIBE from the OpenDTV list in two ways:
>
> - Using the UNSUBSCRIBE command in your user configuration settings at
FreeLists.org
>
> - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
unsubscribe in the subject line.
>
----------------------------------------------------------------------
You can UNSUBSCRIBE from the OpenDTV list in two ways:
- Using the UNSUBSCRIBE command in your user configuration settings at
FreeLists.org
- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
unsubscribe in the subject line.
Other related posts:
