PAL SVCD - Optimal resolution for preserved aspect ratio?

[Gew]

Hiya!

Real quickie-question from a rather novice noobie here. When authoring DVD's, you do best in taking concern in the slight difference in sample aspect ratio between computer monitors and PAL television sets. A PAL DVD is 768x576 from 4:3 resolution. However, this is only, what to call it.. a "virtual" way of describing it, since pixels aren't the same at all. However, the thing is that to author DVD's without aspect rate loss, it's told that you shall use i.e. 720x576.avi content for 4:3; 720x432.avi content for 16:9 PAL DVD.

Now, to my issue...

What's the deal with PAL SVCD's? The resolution on these seem disorted as can be. So, 480x576 for instance, the 4:3 PAL SVCD "output". What resolution should my "input clips" have? Some sort of table would be much appreciated!


Regards~

[tomlee59]

Someone has horribly misled you. A PAL DVD can be 704 or 720 x 576, never 768x576. There is an inherent difference between the "pixel aspect ratio" (obtained by simple division of one number by the other) and the "display aspect ratio" (which accounts for the possibility that the pixels are not square). You seem to think that a DVD has square pixels, so that 768/576 equalling 4:3 is the right math. Nope; that ain't the way it is.

I'm not sure what you mean by svcd's being "as distorted as can be." They play fine on my players. Perhaps if you describe more carefully your actual workflow, and the method by which you are evaluating the result, we can diagnose your problem.

You may also benefit by clicking on "What is DVD" and "What is VCD" in the upper left-hand corner and studying what the actual specs are for the various types of discs you are talking about. If you get that wrong, you'll have no end of troubles.

[Gew]

Well, I hope I'm not all that misled after all. I realize that PAL uses non-square pixels. My english isn't so good, perhaps I just wasn't able to explain my workflow enough. I mean like, 720x576 is not 4:3, but 5:4. Still, 720x576 computer video clips thrown in DVD format shown as perfectly 4:3 on the screen. I have therefor come to figure that somehow the SAR of 12:11 is what's linking the 5:4 (computer screen) / 4:3 (pal tv set) DARs to make perfect match. Furthermore, the 768x576.. Like I said,, "a virtual way of describing it".. The latter relationship of SAR/DAR's, I mean. Hmm, hope I made myself understood. Anyways, I'm not all up in blue, yet noobisch.

Now, as for what SVCD goes..
480x576 is the output (12:11 SAR I presume) resolution. Now, by "disorted", I mean more like.. well.. not that it's anything wrong with it.. but just that it's "for man kind unlogical". Hope I made sense there. I mean, the "width x height" relationship usually comes from a greater width than height, right.. Now.. I have come to understand that SVCD-compilant playback devices "stretch" the image to correct 4:3 DAR, just like DVD (whereas 5:4 DAR --> 4:3 DAR). However, the stretching here must be so much more. I mean, hmm.. 480/576=0,83333333333333333333333333333333. I mean like.. 768-480=288 pixels of width stretch, right?

Then..
Let's say I have this 640x480 (square pixel SAR / 4:3 DAR) videoclip.avi that I want to pull an SVCD image out of. What to do then? Will I like.. err.. Lanscoz3-shrimp it down to .. err.. well I can't do the calculys by hand I'm a bit slow-minded... but you get the deal.. I mean, drag it down to a DAR of 0,834? Or..? Hmm, hold up.. I still need to transcode to SVCD then, right? Maybe the util that does this for me (usually??) also handles the DAR-issue in the best way possible?

I'm a bit confuzed here. I sort of rounded myself into a corner. This last (possible???) state of de facto of mine maybe even answered my original question. Let's see now, how I will wrap this up. Ok, I think I got it. Down below here:

My question:
(the wrap-up)
I have 640x480videoclip.avi which obviously is square pixel 4:3. Now I want to author a SVCD out of this. I fetch some GNU softwarez and get to the chase. I click "import video data" or something like that, and chose the .avi file I just told you about. Then I click MAKE SVCD!! and go to eat meanwhile. Now, will the softwarez resize my .avi to.. hmm.. well 0,83333... so that my stand-alone SVCD player device can (once again) streeeetch it out so that it will show (F)ull(S)creen style on my old 4:3 PAL tv set.


Thank you in advance for helping a poor boy out!

Someone has horribly misled you. A PAL DVD can be 704 or 720 x 576, never 768x576. There is an inherent difference between the "pixel aspect ratio" (obtained by simple division of one number by the other) and the "display aspect ratio" (which accounts for the possibility that the pixels are not square). You seem to think that a DVD has square pixels, so that 768/576 equalling 4:3 is the right math. Nope; that ain't the way it is.

I'm not sure what you mean by svcd's being "as distorted as can be." They play fine on my players. Perhaps if you describe more carefully your actual workflow, and the method by which you are evaluating the result, we can diagnose your problem.

You may also benefit by clicking on "What is DVD" and "What is VCD" in the upper left-hand corner and studying what the actual specs are for the various types of discs you are talking about. If you get that wrong, you'll have no end of troubles.

[minidv2dvd]

don't make this more complicated than it is. if you have a 4:3 640x480 25fps avi and want to make it into svcd, then just encode it to svcd spec fullscreen mpeg-2 at 480x576 25fps. the player will display it properly.

[tomlee59]

I'm a bit confuzed here. I sort of rounded myself into a corner. This last (possible???) state of de facto of mine maybe even answered my original question. Let's see now, how I will wrap this up. Ok, I think I got it. Down below here:

My question:
(the wrap-up)
I have 640x480videoclip.avi which obviously is square pixel 4:3. Now I want to author a SVCD out of this. I fetch some GNU softwarez and get to the chase. I click "import video data" or something like that, and chose the .avi file I just told you about. Then I click MAKE SVCD!! and go to eat meanwhile. Now, will the softwarez resize my .avi to.. hmm.. well 0,83333... so that my stand-alone SVCD player device can (once again) streeeetch it out so that it will show (F)ull(S)creen style on my old 4:3 PAL tv set.


Thank you in advance for helping a poor boy out!

That's why I asked you about your workflow details. If the software you are using to perform the conversion is at all well-written, you should not have to worry about all this higher-order math (which seems only to confuse you). You specify the source, and then you specify the target, and the software should do the rest correctly.

As minidv2dvd said, there's no need to complicate this the way you have. Properly written software will understand how to preserve the correct display aspect ratio during the transcode -- that's sort of the purpose of software, to unburden the user from having to evaluate tensors just to make the output look right.

[Gew]

Thanks!

[Gew]

I'm back.
Sorry..

When I went to sleep yesterday night, I finally managed to address my thoughts into a somewhat meaningful sentence. So, I'll try again, hoping for someone to catch me with a pleasant answer. So, here goes nothing.

When authoring PAL DVD project, you are supposed to use clips of i.e. 720x576 resolution, a DAR of 5:4 whatsoever. In the outcome DVD these will be shown in perfect 4:3 DAR on PAL TV sets.

Now, when it comes to SVCD. What's the deal here? Someone told me that throwing 640x480.avi into a PAL SVCD project will make the result a perfectly match on 4:3 TV set. This means 4:3 square --> 4:3 PAL (12:11), in contradiction to DVD project transfer of 5:4 --> 4:3.

So, I just want to make sure. Is 640x480.avi really the clip to throw on my SVCD project? Are you sure that I'm not really supposed to use 640x512.avi (which is 5:4 square pixel)..?

OR, will "majority of SVCD authoring software" i.e. bloatware Nero simply respond to either 5-4.avi clips or 4-3.avi clips, resulting in perfect match á 480x576 SVCD, displaying perfectly well as 4:3 on my PAL TV set, regardless of whether I use 5-4.avi or 4-3 as for input?

[tomlee59]

Welcome back, Gew.

Perhaps the following link will be of some help in clarifying the situation: http://www.doom9.org/index.html?/aspectratios.htm

It seems to be well written, so hopefully it will answer your questions thoroughly. Note that it alludes to the inability of certain software players to get DAR correct in some instances (WMP is an example). However, software players like VLC generally get it right, and even if it makes a wrong guess (e.g., if an improper DAR flag was set), you can override its aspect ratio (and cropping) choices to make the displayed result correct.

If viewing the result on a dedicated standalone player, then the conversion software bears the responsibility for performing the correct conversion. I have not used Nero for this purpose (in general, I dislike Nero, as it is very poorly written), but I would not be surprised if it gets things wrong.