converting 592 wide avi - upsamp to DVD or downsamp to SVCD?

[LisaB]

They tell you that you should never upsample resolution when converting, but I don't think I've ever actually seen a 720 pixel wide AVI anywhere....that would mean you should never convert an avi to dvd resolution!

I have some movies in divx format that take up 2 complete CD's! They are beautiful dvd-quality, and I would think they should be converted to DVD-resolution not SVCD-resolution, but I think even they are only 640 pixels wide.

[Gazorgan]

You won't see a 720x480 AVI, you will see a 640x480 AVI for a 4:3 .

AVI's have a DAR of 1:1, so 640x480 is 4:3. Did you ever wonder how a 720x480 DVD is 4:3, or 16:9, or Anamorphic? It's called DAR or Display Aspect Ratio and it's why some movies look tall/skinny or short/fat.

What is the real resolution of your AVI?

[bugster]

If you think the quality of the movie is worth a whole DVDr, then encode it at 720*480. The resizeing may not be perfect but chances are you won't notice much if at all.

[LisaB]

I do understand AR considerations, which is why I was only referring to width. A 16x9 avi with 720 width would have 405 height.

During the conversion to DVD res, the physical pixels of a 640x480 avi will have to be interpolated to create a MPG that is 720 wide. This would be upsampling.

However, the aforementioned 16x9 avi would not have to be upsampled horizontally, and would actually need to be slightly *downsampled* vertically from 405 to 360 (with black bars added to make 480).

Now, a 640 wide 16x9 avi would have height 360, meaning that it would not have to be resampled vertically, but it would have to be *upsampled* horizontally.

So, for a 16x9 avi, the issue of 720 wide vs. 640 wide comes down to whether you would rather upsample horizontally or downsample vertically.

As far as I know, you should use bilinear algorithms to downsample and bicubic algorithms to upsample. I don't know what the other tradeoffs are.

I'm guessing I should convert to DVD for anything with 592 or greater width, and to SVCD for widths between 352 and 592, and to VCD for widths 352 and below....make sense? I just wonder if this is the common logic or not, and if there are any special techniques for high-quality upsampling.

[Gazorgan]

Ummm, sort of. Resolutions don't work that way for a DVD. I mean it's clean on paper but it doesn't actually work that way in the dispaly algoythms. It's been explain numerous times on how to keep the heads from being fat/skinny before you change the size.

An AVI's pixesl are 1:1 . A TV's pixels are 8:9 . If you multiply 720x480 by a TV's 8:9 pixel size you get 640x480. That's why I said 640x480 AVI is the same as 720x480 MPEG. The vertical is the same, but the horizontal is skinnier. This is why true resizing usually involves padding/cropping then a resize.

And you still didn't give me the AVI's resolution.

Assuming it's 592x444 (it can't be 333, DivX won't do that), try this.

Reisize it in VDUB to 640x480. You are looking at a 7% increase, and that's not very much. Going dow to 352x480 would be 40% reduction, which is a LOT! Frameserve it to TMPGEnc. Set TMPGEnc to take the input as 1:1 VGA, Maintain Aspect Ratio, (I assume its 23.97 fps) 23.97 fps and set the 3:2 pulldown.

Output should be 720x480 DVD video. Try CQ to hit your target size of 4.1 GB for video+Audio (overhead, don't forget overhead).

That's the best I can do from work off the top of my head p

[LisaB]

Agreed about the NTSC TV's pixels...which is why a 720x480 pixel MPEG, when viewed on a TV, has a 4:3 aspect. However, that same 720x480 pixel MPEG, when viewed on a PC (via PowerDVD, for example), also has a 4:3 aspect....this is because of the embedded aspect ratio tag which the software player sees....after it sees the tag, it does on-the-fly scaling so that the aspect comes out right on the PC.

The point I am trying to make is that the MPEG above actually has 720x480 pixels, *not* 640x480. It is the software player that does on-the-fly scaling, not the standalone DVD, thus when you create a DVD MPEG, you must create a 720x480 pixel MPEG. At least this is what I always thought, and I may be wrong.

So if you want to convert a 592x444 AVI (which is always 1:1), then you can do one of two things:

1. input AVI directly to TMPGEnc and set source aspect to 1:1

or

2. resize to 720x480 using VirtualDub or AVISynth and set source aspect to 4:3

Presumably, one would choose option 2 because they think VDub/AVISynth has a higher quality scaling routine.

However, I do *not* see the point in resizing to 640x480 and setting source aspect to 1:1. This will work, but this will still require scaling (at least in one dimension) within TMPGEnc to create the 720x480 output.

Anyway, I'll throw in one more caveat regarding downloaded AVI's, many of which have dubious quality, and who knows how they were made....

I have come across a number of 352x240 AVI's out there. As far as I know, AVI's don't have aspect ratio tags, and so a PC software player would presumably play them using the standard 1:1 VGA aspect. However, in almost every case these AVI's actually have a 4:3 aspect. Since 352/240 is almost equal to 4/3 it is probably not noticeable, but when you use a 352x240 AVI in TMPGEnc, you should probably make sure to set source aspect to 4:3. This is of course more crucial for PAL 352x288 AVI's.