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Posted by Jukka Aho on 12/13/06 07:29
Max Haltermann wrote:
> Thanks for the pointer re aspect ratio terms.
> As I wrote in my first posting, the transmitted signal of all local
> DTV stations has 4:3 images embedded in a 16:9 transmission. Format
> 12P16
> VideoRedo File info says 16:9 and image 720:576 (normal PAL format).
>
> This makes sense for the DTV stations, as this way they provide both
> main aspect ratios for the end user.
It doesn't make too much sense to me - and that's exactly why I asked
for a clarification. :)
You're hailing from .au, and you're using the same DVB standard for
digital tv as we do here in Europe. The DVB standard allows aspect ratio
signalling: pictures can be sent in 12F12 format or in 16F16 format and
signalled respectively.
My local stations send their programming in their original full-frame
format (be that 12F12 or 16F16), without adding any bars. While doing
this, they also signal the correct aspect ratio. The tv set (or the DVB
viewer program on a computer, if you're using a DVB tuner card)
auto-switches the aspect ratio according to this signalling. The benefit
of this approach is that the viewer will get the full original
resolution all the time, without having to deal with compromised
downsampled images with the black bars and loss of resolution.
(Granted, sometimes you'll see 12P16 segments within a 16F16 programme,
or 16L12 segments within a 12F12 programme, but they're usually just
short inserts that were sourced in a different format - archive
material, for example - and not the main bulk of the programme.)
> So the question still is: How can one get a full hight and full width
> 4:3 display from the raw digital TV transmissions on to DVD
> or onto a TV screen, seeing there is no D/A conversion or decoding
> involved?
Another poster already suggested using IFOEdit and applying the "pan &
scan" feature [1] of the DVD-Video standard. This sounds like a good
solution to your problem as it doesn't require re-encoding the image.
(Since the active area of your 12P16 image is centered and nothing
happens outside that center area, you don't need to actually define any
pan & scan vectors. Just switching the mode on will be enough.)
If the 12P16 MPEG stream is flagged this way - as "pan & scan"
material - and if the DVD player is set up for a 4:3 display, this
method will (or at least should) create a centre cut-out of the 12P16
picture and zoom it to cover the full screen.
(In other words, the player will convert the image back to its original
12F12 format, on the fly.)
The horizontal resolution that was lost when the station originally
converted the 12F12 picture into a 12P16 format will unfortunately stay
lost forever. But at least you'll get a full-screen picture on a 4:3 set
instead of a postage stamp with black borders on all sides.
_____
[1] See <http://www.dvddemystified.com/dvdfaq.html#3.5> and the
paragraph that begins with "For automatic pan & scan mode..."
--
znark
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