4:3 vs 16:9

[travis morgan]

will a movie with an aspect ratio of 4:3 encode better (higher quality) to vcd than a movie with an aspect ratio of 16:9?

i'm assuming it will, due to my divx experience, because the black bars will be cropped off.

right or wrong?

[Taric25]

There is no cropping in VCD like Divx. 4:3 widescreen movies (unlike DivX) have the blck bars encoded in them. It's kind of hard to encode a 16:9 VCD (I suggest SVCD) but 16:9 would have no black bars to encode useless bits, so it would look better.

[travis morgan]

i think i worded my post wrong. does 4:3=fullscreen? if its full screen then there wouldn't be any black bars right? i understand you can't crop vcd's or svcd's. i prefer svcd's, but my buddy's dvd can't play them so i'm making him a vcd. so, would a fullscreen movie encode better to vcd than a widescreen movie?

does this make more sense?

[zambelli]

First of all, we must clarify that we're taking about letterboxed widescreen here, and not anamorphic widescreen, right?

It's a good question. Personally, I think the widescreen movie would encode better BECAUSE of the black bars. Why? Well, with a fullscreen movie there would be 16M colors covering the full 352x240 screen in every frame and thus the bitrate would have to be distributed over those 352x240 pixels. However, with black bars on top and bottom, I think most of the bitrate would be distributed over the 352x192 (or whatever it is) area, since it doesn't take much to encode the single colored bars that take up the rest of every frame. Isn't that how JPEG (and thus probably MPEG) compression works? An image containing 10 colors compresses more than an image containing 16 million colors, right?

[travis morgan]

zambelli,

but isn't that what you want...the bitrate going towards the picture and not the black bars.

isn't that why we crop the black bars off for divx?

[twistee]

i never thought about it like that...i always thought you cropped the bars off because it looks nicer and more 'professional' to have just the movie....but cropping it off so the picture is better makes sense.

[zambelli]

Travis,

Yes, we cut black bars from DivX movies so that we wouldn't waste bitrate on black bars. But that's not the question with VCD: the question is whether fullscreen movies encode better or worse than letterboxed widescreen movies, where cropping is not an option. If we could crop VCD movies, I'm sure we would. :)

Look at it this way: encoding NOTHING (cropped DivX) is better than encoding BLACK BARS (uncropped DivX), so I say encoding simple BLACK BARS (letterboxed VCD) is better than encoding MOVING IMAGE (fullscreen VCD). "Better" in this case means "doesn't waste bitrate".

Does that make senes to anyone else? These are merely my subjective conclusions, and are not based on any studies or reports that I read. Of course, my whole thoery is based on the assumption that MPEG encoders are smart enough not to waste too much bitrate on monochrome bars. When we crop DivX movies, we force the encoder to only encode the moving part of the image. With VCD, I certainly hope that the encoder spends only a fraction of its bitrate on black bars and the waste majority of it on the moving image.

[Taric25]

I suggest that everyone reads Aspect ratios in DVD basics on Doom9's site.

[zambelli]

Why would we? What has so far been unclear or incorrect?

[Taric25]

Everything has been clear, but I want to make sure, not just for the people posting, but also for the people lurking to know exactly what are talking about.

[Linux]

If you have a TV that is 16:9 and the source is near 1.78:1 then you can make the VCD anamorfic. That leads to no border at all but again since the frame is bigger it uses more bits to be compressed.
Some may say that there is no such thing as an anamorfic VCD but on my TV I have to switch to 16:9 manually anyway.
All recorded media can hold anamorfic movies, VHS too.

[zambelli]

Correct. Most people don't understand that widescreen TVs have controls which allow users to "stretch" 4:3 images horizontally over a 16:9 screen.

[Antonio S.]

zambelli:

You can "stretch" your 4:3 to 16:9 if you have a "Widesreen TV", but if not, you will have a distorted image forever...

Problem is that the (S)VCD standard do not accept 16:9 ratio as output, so sadly we have to insert our 16:9 image in a 4:3 image and loose some resolution (this is oppose to anamorphic widescreen) or crop the image to fill it completely and avoid black bars...

About black bars, when encoding a (S)VCD with black bars you get an smaller mpeg file than when you encode same picture without them (cropping the picture)...

Antonio S.

[Linux]

Antonio S:
You can "stretch" your 4:3 to 16:9 if you have a "Widesreen TV", but if not, you will have a distorted image forever...

Distorted???
My old 4:3 TV that I bought 10 years ago had an option for compressing a picture horizontally to make border on the bottom and top. This made a 16:9 viewable with right aspect.

Forever???
Who is ever going to buy a 4:3 TV anyway.

the (S)VCD standard do not accept 16:9 ratio as output
It does.
There are merely not many DVD-players that understand that.
What do you think a 16:9 anamorfic DVD is anyway?
It is a 16:9 picture squeezed into using all the pixels that usually is treated as being 4:3.
Both a 16:9 and a 4:3 movie use all pixels since they aren’t square.

It is up to the player to correct the anamorfic nature of a 16:9 movie if you tell it that you have a 4:3 TV set. Then it either cuts away the side (pan and scan) or makes it letterboxed.

The DVD that are sold as 16:9 without being anamorfic is actually 4:3 with letterboxing in the movie stream.

My way to see it is the other way around. Once you have got a 16:9 TV you are going to get more anxious about anamorfic SVCD. Most 16:9 TV sets cannot view a 4:3 movie without either:
1. Make wide border on the side.
or
2. Enlarge the movie so that you both loose quality and having trouble while reading subtitling.
Or
3. You get the wrong aspect ratio and some enlargement.

If you are coding your movie with letterboxing (convert from 16:9 to 4:3) than when viewed on a 16:9 TV it must be enlarged. This is when you understand why the bitrate became lower in the process.

[Antonio S.]

Linux:

Don't take me wrong!!!...I love "anamorphic widescreen" as you do. The problem is that a DVD player can output a 16:9 ratio when playing a DVD and/or a (S)VCD, but the source of a (S)VCD is taken as 4:3. You can find more information on this, here at doom9's guides.

So if doing (S)VCD you will have to deal with 4:3 resolution...

Antonio S.

[Linux]

I hope that you did not get me wrong either ;)

I do not understand your term "the source of a (S)VCD is taken as 4:3" at the same time as you say "a DVD player can output a 16:9 ratio when playing a DVD and/or a (S)VCD".
You say it is this way but not?

This is taken from http://www.forums.pctechguide.com/24dvid3.htm

In common with VCD, SVCD supports 16:9 (anamorphic wide screen) image aspect ratio. However, unlike its predecessor, some SVCD players can signal the TV set to automatically switch to the appropriate mode.

[Antonio S.]

Linus:

What I mean with "source" is the way the (S)VCD is encode. This source may never be 16:9, so you can not do "anamorphic widescreen", and some resolution is lost.
What I mean with "output" is the resolution match between your DVD and your tv set. This means that if you have a regular tv you will set your DVD output to 4:3, and if you have a widescreen tv you will set your output to 16:9. In this last case (widescreen tv) you may get a better resolution if your source is "16:9 anamorphic widescreen"
encoding, than a 4:3 widescreen. As long as I know it doesn't matter what resolution settings (4:3, 16:9, or 1:1) do you do when encoding a (S)VCD it is taken as 4:3...

Antonio S.

[Linux]

Are you sure you understand what anamorfic is?

If you by "output" mean viewing ratio and "source" pixel ratio I think you have misunderstood something.

The pixel aspect in 720x576 is 1.25:1 and the pixel aspect for 480x576 is 0.833:1. This is irrelevant.

If you have a PAL DVD movie encoded as anamorfic 16:9 it uses all 720x576 for stretched pixels. This has a Viewing aspect of 16:9 and has to be displayed on a 16:9 TV by stretching the pixel.
Then you resize the movie from 720x576 to 480x576.
Don’t crop anything and don’t add any borders at all.
This way you actually only compress the width by 3/2.
Now you have a movie that also has a Viewing aspect of 16:9 and also have to be stretched out by the 16:9 TV.

And when you say that the encoding of SVCD is taken as 4:3 you should investigate some more in your encoders about how to set the right switch. In both CCE and bbmpeg it is possible to set flags to indicate which aspect you want. CCE call it DAR 16:9 and bbe just call it Aspect Ratio.

One other aspect nobody talks about is that this single width resize gives a lot better result than shrinking in both directions and borders added.