dvd aspect ratios
 

I'm wondering about dvd aspect ratios.

Does the DVD standard limit DVDs to certain aspect ratios? I'm mostly wondering why DVDs are encoded with black bars, it would seem to be more efficient to just encode the image area and not waste any bits on the black bars and lets the player do the scaling appropriately.

i.e. its generally visible in 2.35:1 DVDs, but my curiosity was peaked by watching Dr. No, which has black bars on the side due to its aspect ratio, which means that it should be able to be zoomed in a little more on most monitors, but it can't.

anyways, just wondering.

If you're seeing black bars on the side of a widescreen TV on a 1.78:1 movie like Dr. No, it sounds like you are watching non-anamorphic DVDs (or your output settings are wrong). Here's a good article that explains it. The links to the photo comparisons about halfway down the page ("Anamorphic vs. Non-anamorphic (1.85:1 Film)" and "Anamorphic vs. Non-anamorphic (2.35:1 Film)") should show you the difference.

http://www.thedigitalbits.com/articl...ge2.html#demos

I am watching it on the new ultimate set (just bought from amazon)

the sidebars are also visible in dvdtalk's review of the film

http://www.dvdtalk.com/reviews/25603...edition-vol-4/

Hence, I doubt its a problem with the player, hence me just wondering what's the point of the studios encoding the black bars in unless the DVD can't have arbitrary resolutions (which might very well be the answer?)

Sorry for the misinformation ... I don't own it, so just did a quick search which incorrectly told me 1.78:1. It looks like it might be 1.66:1. If that's the case, then the side bars on a 1.78:1 monitor are correct and it can't be "zoomed in" without losing some of the image or resizing/misshaping the image.

So, yes, as I understand it DVDs have to be a certain resolution, which is why 2.35:1 films have the thinner black bars encoded on top as shown in the original link I posted.

They can't; the standard NTSC DVD frame resolution is 720x480, for a pixel aspect ratio of 1.5:1. The DVD then has one of two flags to send to the player: a display aspect ratio of 4:3 for full-frame (or non-anamorphic) video, or a DAR of 16:9 for anamorphic video. That flag determines how the player distorts the video frame for display. Any ARs aside from 1.78 or 1.33 need to be matted in some fashion within that 720x480 frame.

though according to a quick perusal of wikipedia, it can also be 704x480. Would seem to be a better choice for those that are matted on the sides.

I suppose a pixel-savings of about 2%--of highly compressible, static pixels, no less--is probably not worth bothering with a less common resolution for relatively rare vertically-matted ARs.

In any case, I think the general assumption is that at least eight pixels on either side of the 720-wide frame are going to be obscured by overscan and the like; it's not uncommon for there to actually be a bit of noise there, depending on the original video source, and I've probably run into more broadcast-derived 4:3 DVDs with eight-pixel-or-so vertical mini-mattes than not.

The ratio in question is 16x9, or 1.78:1. The image on standard DVDs can only be "enhanced for widescreen televisions" at a ratio of 16x9 so the "frame" in question is always 1.78:1, so anything more/less than that ratio will contain some amount of black bars in the encoded picture.

DVD pixels are not square, so therefore the claim that a DVD has a pixel aspect ratio of 1.5:1 is not accurate. A DVD can be either 4:3 (1.33:1) or 16:9 (1.78:1) depending on how the disc is encoded, both at a resolution of 720x480. The 16:9 version stretches the pixels.

PAL DVDs are 720x576 but otherwise work the same way