?'s on AR -- more confused after reading forum topics.

[aram12]

What is the source aspect ratio for SVCD? I've gotten it pounded into my head through the forums that DivX/avi are 1:1, is it also true for SVCD?

Which leads into my real question. Using the standard template in tmpegenc for VCD, I find the preview for the conversion (svcd to vcd) to be a bit anamorphic and with black encoded on top, bottom, AND sides. This is with Full Screen (keep AR) selected. Why is this? I understand that I shouldn't trust the tmpegenc preview, but it just doesn't seem to make sense to me.

And on another note, would someone please explain once and for all the difference between pixel aspect ratio and display aspect ratio as it relates directly to VCD, SVCD and DivX/Avi video formats, their conversion and the corresponding settings in tmpegenc? I did a search on the topic in the forums and there is a lot of conflicting information.

I'll give out something I'm confused about just to get the ball rolling...I understand that the preview in tmpegenc when converting to SVCD (and Video ---> AR is 4:3) is square and the actual video data itself is stretched on the vertical because SVCD resolution is 480 x 480, but it is being encoded to be played on a 4:3 display aspect ratio (your 1.33 TV set). Thus when the stretched video is played on your TV, it is "fit" to the AR of the TV (4:3) and the pixels, in effect, become rectangles, maintaining the 480x480 resolution. Is that right?

Urg, I just thought of about 10 more questions, but I'll let the experts do the explaining to start. Thanks in advance. And please be gentle. I have read all the forums topics on the subject and am just still not quite at the level of understanding I want on the subject...

[Mercury]

What is the source aspect ratio for SVCD? I've gotten it pounded into my head through the forums that DivX/avi are 1:1, is it also true for SVCD?

If you mean capturing from SVCD, then it should be a flat-out 4:3 Display (because SVCDs are played on 4:3 displays i.e. TVs).

Which leads into my real question. Using the standard template in tmpegenc for VCD, I find the preview for the conversion (svcd to vcd) to be a bit anamorphic and with black encoded on top, bottom, AND sides. This is with Full Screen (keep AR) selected. Why is this? I understand that I shouldn't trust the tmpegenc preview, but it just doesn't seem to make sense to me.

I'm not sure about this, so I won't comment.

And on another note, would someone please explain once and for all the difference between pixel aspect ratio and display aspect ratio as it relates directly to VCD, SVCD and DivX/Avi video formats, their conversion and the corresponding settings in tmpegenc?

Display AR is the actual movie width vs. height when it appears on whatever medium you're viweing it. This is 4:3 for anything on regular TVs, and 16:9 for widescreen TVs.

Pixel aspect ratio is the pixel width vs. height as it appears on whatever medium you're viewing it. This isn't quite so clear-cut, since it depends on the resolution the video itself is. For example, an SVCD has resolution 480x480, but it must appear in a 4:3 display aspect ratio, so the pixels will have to be 1.33 times as wide as they are tall to fill the screen.

In a CVD, however, the resolution is 352x480, which means the pixels need to be (about) 1.82 times as wide as they are tall to fill the screen.

In a DVD at 720x480, the pixels must be only 0.88 times as wide as they are tall, and so on.

In general, you can calculate pixel aspect ratio using this formula:
(Display Aspect Ratio)/(Horizontal res/vertical res)

In the DVD example:
(4/3)/(720/480)
=(1.33)/(1.5)
=0.88

Usually you'll never have to use this number. Pixel aspect ratio is generally 1 (or 1:1) on a computer screen.

I'll give out something I'm confused about just to get the ball rolling...I understand that the preview in tmpegenc when converting to SVCD (and Video ---> AR is 4:3) is square and the actual video data itself is stretched on the vertical because SVCD resolution is 480 x 480, but it is being encoded to be played on a 4:3 display aspect ratio (your 1.33 TV set). Thus when the stretched video is played on your TV, it is "fit" to the AR of the TV (4:3) and the pixels, in effect, become rectangles, maintaining the 480x480 resolution. Is that right?

Exactly.

I'd like to add one question myself:
In TMPGEnc, if the source aspect ratio is 1:1, TMPGEnc treats it as a pixel aspect ratio, but selecting 4:3 Display, it treats it as a display aspect ratio, right?

[sterno]

In TMPGEnc, if the source aspect ratio is 1:1, TMPGEnc treats it as a pixel aspect ratio, but selecting 4:3 Display, it treats it as a display aspect ratio, right?

Yes.

[aram12]

Mercury-

Ok that helps.

But then why do VCD's when played on a monitor appear "normal"? Wouldn't they ALSO need to be stretched vertically? As then when they played on a 4:3 display (TV) the pixels would be correspondingly adjusted. How does your TV know not to do this? Or does it? What am I missing? I also am realizing it doesn't make sense to say "a VCD played on my computer" as it's not really a VCD, it's an mpeg-1 file, right? And SVCD's are mpeg-2 files...and both aren't really VCD's or SVCD's until they are burned to a disk as such...

I solved my previous issue btw, but I have a new one.

I have successfully converted from SVCD to VCD, but seem to have a shaky frame. This is the whole frame going up and down one pixel every 4 or 5 frames. I switched the starting field and same problem...any ideas?

[Aha, that's really interesting. All the SVCD files I have are shaky. They are shaky in RP and WMP, but play without shake in the Elecard mpeg-2 player. I guess that explains the shake in the VCD conversion. It's at the source. But why the heck does the shake depend on the player?]

[Mercury]

But then why do VCD's when played on a monitor appear "normal"? Wouldn't they ALSO need to be stretched vertically? As then when they played on a 4:3 display (TV) the pixels would be correspondingly adjusted. How does your TV know not to do this? Or does it? What am I missing?

Hmm, if you follow the formula, a VCD pixel ratio (for NTSC) is 1.1:1. Is it at all possible that you're just not noticing the distortion?
VCDs and SVCDs will appear "normal" when played using DVD software, but if you're talking about the MPEG file itself, then I'm at a loss to explain it. It's possible that whatever player you're using can adjust the aspect ratio automatically. (I think some versions of WMP do this?)

I have successfully converted from SVCD to VCD, but seem to have a shaky frame. This is the whole frame going up and down one pixel every 4 or 5 frames. I switched the starting field and same problem...any ideas?

My SVCDs are shaky as well, but since I don't notice it when they're actually played on my DVD, I just dismiss it. My MPEG2 videos also appear upside-down when I use maximum res and color depth, but not when I reduce either.

[aram12]

I'm not seeing the distortion but let me move on.

I still don't think I'm clear on the nomenclature. An SVCD is NOT an mpeg-2, correct? I mean, when I say I'm trying to convert an SVCD to VCD, I think what I mean to say is that I'm trying to convert an mpeg-2 to mpeg-1. I'm not intending to burn. If that's the case, I guess I shouldn't be using TMPGEnc. That is to say, VCD's and mpeg-1's are different and so are SVCD's and mpeg-2's, right?

And if I'm not intending to burn, then does it make more sense to just convert it to mpeg-4? The only piece of software that seems to do that is Vidomi...any recommendations? And dvd2avi doesn't seem to be what I need either as its not an SVCD disc, it's just a single mpeg-2 (svcd, whatever) file I downloaded.

[Mercury]

I still don't think I'm clear on the nomenclature. An SVCD is NOT an mpeg-2, correct? I mean, when I say I'm trying to convert an SVCD to VCD, I think what I mean to say is that I'm trying to convert an mpeg-2 to mpeg-1. I'm not intending to burn. If that's the case, I guess I shouldn't be using TMPGEnc.

First of all, you can use whatever porgram you like, there's nothing that says TMPGEnc is only for (S)VCDs. And yes, SVCD and MPEG-2 are different things, but it's easy to start using them interchangeably, which of course you shouldn't.

And if I'm not intending to burn, then does it make more sense to just convert it to mpeg-4?

I can't say since I don't have experience with it.

not an SVCD disc, it's just a single mpeg-2 (svcd, whatever) file I downloaded.

Now, for the purposes of converting, it's important to know whether this is a "SVCD-ready MPEG2" or just an regular MPEG2 designed for computer viewing (since these two will have different aspect ratios onscreen).

[aram12]

Thanks for all your help. Things are a bit clearer now.