[opendtv] Re: BBC Demonstrates HDTV Broadcasts over SD Channels
- From: "John Shutt" <shuttj@xxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 23 Jun 2005 12:25:55 -0400
John,
ATSC table A3 does not allow 640x480 with a display aspect ratio of 16:9. I
have no idea if MPEG2 allows 640x480 16:9. ATSC table A3 specifically
allows only 4:3 format for 640x480.
What you are looking for is a 480 line 16:9 format with square samples,
which does not exist in ATSC. The absence of square samples does not
preclude the display of 16:9 pictures.
John
----- Original Message -----
From: "John Willkie" <JohnWillkie@xxxxxxxxxxxxx>
> 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.
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