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DVD Aspect Ratio Question

 
 
George Graves
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Posts: n/a
 
      12-08-2005
I have a technical question about DVD aspect ratios. I'm not sure
exactly how to phrase it so that it's clear, but I've come here because
I can find nothing on the web that covers this.

As you probably know, many HDTVs and HD-ready sets automatically assume
that any time they see a component video input that has a 31.5KHz raster
or higher, it's indicative of a high-definition program. This causes the
TV to automatically apply the anamorphic stretch to the standard NTSC
4:3 frame to make it 16:9. In some sets, this anamorphic stretch is user
defeatable, but in most, it is not.

Most modern DVDs made from old TV shows, older, non-widscreen movies, or
even DVDs that have the widescreen picture letterboxed rather than
anamorphically squeezed, display the progressive picture output fine on
sets where the anamorphic stretch can not be defeated, but other DVDs
will display the progressive output as 16 X 9 when they should display
it as 4:3 - with the inevitable distortion to the picture, of course.

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?

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.

Thank you in advance for any insight into this phenomenon that you can
give me.
 
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Joshua Zyber
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      12-09-2005
"George Graves" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ...
> 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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George Graves
Guest
Posts: n/a
 
      12-09-2005
In article <2f4mf.1121$(E-Mail Removed) >,
"Joshua Zyber" <(E-Mail Removed)> wrote:

> "George Graves" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) ...
> > 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.


Thank you for your answer. I'm going to assume, based upon what you have
said, that 4:3 content DVDs which come out stretched on the same DVD
players which set the aspect ratio correctly on other 4:3 content DVD
discs does so because these discs either lack the proper flag, or the
flag is set incorrectly (many of the discs which do this in my
collection are older from 1998, 1999, etc.

--
George Graves
 
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Joshua Zyber
Guest
Posts: n/a
 
      12-09-2005
"George Graves" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ...
> Thank you for your answer. I'm going to assume, based upon what you
> have
> said, that 4:3 content DVDs which come out stretched on the same DVD
> players


Just to clarify, it's not the DVD player doing the stretching. It's the
TV. The DVD player outputs the original 720x480 pixel video image, which
the TV is *supposed* to allow you to adjust.

> which set the aspect ratio correctly on other 4:3 content DVD
> discs does so because these discs either lack the proper flag, or the
> flag is set incorrectly (many of the discs which do this in my
> collection are older from 1998, 1999, etc.


That's a reasonable assumption.


 
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Captain Jinks
Guest
Posts: n/a
 
      12-11-2005
Why don't you take your question up with several of the major hardware
manufacturers and see what they say rather than ask a forum full of
novices? Frankly it doesn't sound like you know enough on the subject to
review any equipment that I'd want to buy.

Jinks


In article <gmgraves-900EB5.07320808122005
@newsclstr02.news.prodigy.com>, http://www.velocityreviews.com/forums/(E-Mail Removed) says...
> I have a technical question about DVD aspect ratios. I'm not sure
> exactly how to phrase it so that it's clear, but I've come here because
> I can find nothing on the web that covers this.
>
> As you probably know, many HDTVs and HD-ready sets automatically assume
> that any time they see a component video input that has a 31.5KHz raster
> or higher, it's indicative of a high-definition program. This causes the
> TV to automatically apply the anamorphic stretch to the standard NTSC
> 4:3 frame to make it 16:9. In some sets, this anamorphic stretch is user
> defeatable, but in most, it is not.
>
> Most modern DVDs made from old TV shows, older, non-widscreen movies, or
> even DVDs that have the widescreen picture letterboxed rather than
> anamorphically squeezed, display the progressive picture output fine on
> sets where the anamorphic stretch can not be defeated, but other DVDs
> will display the progressive output as 16 X 9 when they should display
> it as 4:3 - with the inevitable distortion to the picture, of course.
>
> 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?
>
> 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.
>
> Thank you in advance for any insight into this phenomenon that you can
> give me.
>

 
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Richard C.
Guest
Posts: n/a
 
      12-17-2005
X-No-archive: yes

"George Graves" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ...
>I have a technical question about DVD aspect ratios. I'm not sure
> exactly how to phrase it so that it's clear, but I've come here because
> I can find nothing on the web that covers this.
>
> As you probably know, many HDTVs and HD-ready sets automatically assume
> that any time they see a component video input that has a 31.5KHz raster
> or higher, it's indicative of a high-definition program. This causes the
> TV to automatically apply the anamorphic stretch to the standard NTSC
> 4:3 frame to make it 16:9. In some sets, this anamorphic stretch is user
> defeatable, but in most, it is not.
>

==========================================
My HD set does not do that.
Many that I have seen do not do that.....................
Most show the 4:3 frame within the 16:9 screen (in proper ratio).
You must have your settings wrong.
-----------------------------------------------------------------

 
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