Posted by Joshua Zyber on 12/09/05 00:30

"George Graves" <gmgraves@pacbell.net> wrote in message
news:gmgraves-900EB5.07320808122005@newsclstr02.news.prodigy.com...
> My question is simply this. Why is it that some 4:3 DVDs get stretched
> to 16:9 when played on a progressive player (irrespective of what one
> does with the "aspect ratio" controls in the set-up menu) while other
> 4:3 DVDs don't get stretched? Is there a 'bit' that can be set in the
> DVD headers at mastering which tells the player that the picture is
> 4:3,
> and when that bit isn't set, the player outputs the picture as 16:9?
> Or
> is the content of the discs that display correctly mastered
> anamorphically squeezed complete with side-bars? If the latter, how
> come
> they still look correct when played back on a normal NTSC monitor
> using
> composite or S-VHS inputs?

It would help if you could specify which DVD player is being used and
what DVDs.

All DVD video contains 720x480 pixels in a native 4:3 format (DVD pixels
are not square). Anamorphic widescreen discs are mastered in such a way
that the image is stretched vertically, and if viewed on a 4:3 TV
without proper downconversion will look distorted. However, when viewed
on a widescreen TV this anamorphic image will be stretched horizontally
to restore the proper picture geometry, but the resolution is still
720x480 pixels.

The problem you describe occurs when you upscale DVD video to a higher
resolution such as 720p or 1080i (and on many older sets is problematic
with 480p as well). The TV sees the higher number of pixels coming in
and thinks, "Ah ha! This is an HDTV signal. All HDTV is natively 16:9.
Therefore, I must automatically lock into 16:9 mode." Of course, not all
DVD content is natively 16:9, so when the TV enforces this stretch
you're left with a distorted 4:3 image.

The answer to your question is yes, DVDs contain an aspect ratio flag
that indicates whether the disc is 4:3, 4:3 Letterbox, or 16:9.
Unfortunately, many discs are incorrectly flagged, and you see a lot of
4:3 Letterbox discs that are flagged as plain 4:3.

*Some* DVD players (certainly not all, nor even a majority) have the
ability to read this flag and offer automatic aspect ratio control when
viewing on a 16:9 TV. In other words, if the TV is 16:9 but the disc is
flagged as 4:3, the player will automatically scale the image down to a
540x480 square and put black pillarbox bars on the sides, thus allowing
you to watch 4:3 content in its correct aspect ratio on your screen,
though at the cost of lower resolution and less picture detail. Again,
many discs are incorrectly flagged, so this is not a 100% foolproof
operation. Additionally, if the disc is correctly flagged as 4:3
Letterbox, some of these DVD players with aspect ratio control can zoom
it to fill the screen, but others treat all 4:3 material the same and
you wind up with a small picture with black bars on all 4 sides.

> I need to know this because I review a lot of DVD players for an
> on-line
> video magazine and I've not seen ONE player that will allow some of
> these 4:3 DVDs to display properly when output progressively or
> up-sampled and I'm at a loss to explain exactly why this happens.

The Oppo OPDV971H is a player that offers automatic aspect ratio control
for upsampled DVDs. The mode is called "Wide/SQZ" in the set-up menu.
The mode defaults to only pillarboxing the content, but there is a
manual zoom you can engage for 4:3 Letterbox discs. Unfortunately, there
is a significant loss in quality when using the zoom.

Another, though more expensive option, is to use a video processor or
HTPC that will allow you to manipulate the image in all sorts of ways.

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