4:3 to 16:9 pillarboxed

[hello_hello]

This DVD aspect ratio thing always does my head in. Are we actually talking about the same thing here?

Cornucopia, you appear to be referring to the resolution of the video itself in terms of resizing (720x480 or 704x480). Is that correct? 704x480 is a valid resolution for 4:3 isn't it? So yes, it makes total sense a player should know the difference between video with a width of 720 and 704 and still resize them both to 4:3. I don't think I'd argue with you there. Is that basically what you're referring to?

When Island_Dweller said he has "music video DVDs with PAR 10:11 which MPC-HC assumes to have PAR 8:9"..... I assumed he was referring to 720x480 video which is being resized to 640x480 but he feels it should be resized to 654x480. When I referred to all software players resizing with a 8:9 pixel aspect ratio, that's what I was referring to (to be honest I'd forgotten 704x480 is a valid DVD resolution for 4:3).... and basically what you said.... for a 720x480 4:3 DVD there's no way to tell if the active picture area is supposed to only be 704 wide.... in fact I have some old 4:3 DVDs here which have a nice row of pixels down each side which to me implies if there's any order in the universe they must use a 10:11 pixel aspect ratio.... but I'm fairly certain they don't (well they're PAL DVDs but the same principle applies).

I'm fully prepared to stand corrected on this, because as I said, this whole DVD pixel aspect ratio thing does my head in so I try not to think about it. To the best of my knowledge if a DVD has a 720x480 resolution, every software player I've ever met will resize it to either exactly 4:3 or 16:9 dimensions.
I know you wrote 16:9 a few times in your last post but we are referring to 4:3 DVDs when talking about 10:11 and 8:9 pixels aspect ratios?

There's a whole bunch of stuff regarding DVD resizing I don't quite understand, so maybe it's time someone explained it to me. For instance I get the whole analogue to digital thing... well maybe as much as I want to.... and the 704x480 or 702x576 thing is a result of a standard for sampling an analogue signal, but I'm still not really sure I understand why there's a resizing ambiguity.... ie why mostly a straight 4:3 or 16:9 resizing is used these days rather than the ITU method for 720x480 video.

Or even the difference in 4:3 and 16:9 specs..... as I understand it, HDMI 4:3 and 16:9 are actually 4:3 and 16:9 and I'm sure I recall reading the odd thread where someone had tested their HDMI Bluray player to discover the video is resized differently according to whether the composite or HDMI output is used.

About the only thing I am fairly confident about (well in PAL-Land, at least) is the way you need to resize the majority of DVDs these days to obtain the correct aspect ratio, and it's definitely not ITU. I've compared quite a large number of old DVD to Xvid/AVI encodes with their Bluray counterparts, where ITU resizing was not used when encoding, and my OCD tenancies eliminated any resizing aspect ratio distortion as much as humanly possible, and in by far the majority of cases my old DVD encodes have the same aspect ratio as the Bluray version. In fact I can only recall a couple of times when I compared the old DVD encode and thought.... "whoops, I guess that one should have been ITU".

Anyway, if you can enlighten me a little regarding the history of DVD resizing I'll be happy to learn. Much of the time when discussing this sort of thing in forums it's hard to work out who really knows what they're talking about and who doesn't.

[Island_Dweller]

Well, short of indexing your dvd with dgindex and saving a frame with round objects, then trying both ITU and non-ITU resizing with a picture editor, there are 2 possible PAR for NTSC and 3 for PAL.

NTSC will either have PAR 10:11 or 8:9 for 4:3 and 40:33 or 32:27 for 16:9.

PAL is more complicated. The non-ITU PARs are 16:15 for 4:3 and 64:45 for 16:9.

For ITU, please read this http://en.wikipedia.org/wiki/Pixel_aspect_ratio#Background

Basically, PAL should use PAR 59:54 for 4:3 and 118:81 for 16:9.

But to get PAL 4:3 at exactly 704x576, the 59:54 is adjusted to 12:11 (60:55)
Similarly, to get PAL 16:9 at exactly 704x576, the 118:81 is adjusted to 16:11 (120:82.5)

My rule of thumb is : if a video is padded on the left or on the right (or both), ITU resizing should be used (but not always ).

I think that before BluRay production started, quite a few DVDs used ITU PAR. But with Bluray requiring a 16:9 picture, it became more convenient to make a 16:9 master and use that for both BD and DVD.

Also, both you and Scott have made valid points. TMPGEnc products, Adobe and even Apple Quicktime use ITU PAR for resizing SD MPEG-2. But most free software players use non-ITU by default.

[jagabo]

DVD only specifies the frame size and the DAR. With commercial NTSC DVDs I've only ever seen a frame size of 720x480. The only two DAR that can be flagged directly* on DVD is 4:3 and 16:9. So, by the spec, the only two PAR on NTSC DVD are 8:9 and 32:27.

When analog video is captured the equipment usually follows the ITU specification. The 4:3 or 16:9 picture is captured with a 704x480 frame, giving a PAR of 10:11 (4:3) or 40:33 (16:9). If a 720x480 frame is used the PAR doesn't change -- the extra 16 pixels are just padding. So the DAR for the entire 720 pixel wide frame is slightly wider than 4:3 or 16:9. From what I've seen, when that 720x480 frame is made into a DVD the difference in PAR is usually ignored. The frame is usually taken as-is and flagged, incorrectly, as 4:3 or 16:9 DAR. And that's why we're all here having this discussion.

If you're a real stickler for aspect ratios you'll examine the video yourself and see which PAR should be used when you rip the DVD. But nobody can see the ~1% the difference without measuring an object with known aspect ratio on the screen. If you're using an analog CRT the TV's aspect ratio error is probably larger than 1 percent so you won't get an accurate measurement. On a computer you can count the pixels across the width and height (obviously, any image editor can do the counting for you).

In my opinion, if the DVD producer doesn't care about the difference, why should I?


* The DVD spec does have a mechanism by which ITU PAR could be specified, the Sequence Display Extension. So a 720x480 ITU frame could be used and the Sequence Display Extension could indicate that the 4:3 or 16:9 DAR picture is contained in the inner 704x480 sub frame. But I've never seen this on a commercial DVD. The only time I've seen it used is when the DVD is flagged 4:3 DAR and the Sequence Display Extension specifies a 540x480 sub frame contains that DAR. Which means the full 720x480 frame is 16:9 DAR.

[hello_hello]

When analog video is captured the equipment usually follows the ITU specification. The 4:3 or 16:9 picture is captured with a 704x480 frame, giving a PAR of 10:11 (4:3) or 40:33 (16:9). If a 720x480 frame is used the PAR doesn't change -- the extra 16 pixels are just padding. So the DAR for the entire 720 pixel wide frame is slightly wider than 4:3 or 16:9. From what I've seen, when that 720x480 frame is made into a DVD the difference in PAR is usually ignored. The frame is usually taken as-is and flagged, incorrectly, as 4:3 or 16:9 DAR. And that's why we're all here having this discussion.

I'm still trying to get my head around that. Even if only 704x480 of the 720x480 frame is active picture area, if it's transferred to DVD using a 720x480 frame then I'm not sure where the aspect ratio is flagged during the process or where the aspect ratio comes into it. Given the official DVD resizing method is slightly wider than 4:3, resizing it that way should resize it correctly. Unless I'm missing something.
Now if you were to take the original 704x480 frame and transfer it to a 720x480 frame without correcting the aspect ratio (ie adding the black borders) then a DVD player wouldn't resize it correctly, but resizing it to exactly 16:9 would be correct given the original 704x480 video was intended to be resized that way. That wouldn't account for the 720x480 DVDs with only 704x480 of active picture area which still seem to want to be resized to exactly 4:3 though. Or am I missing something?

Logically to me, where the aspect ratio would most likely go wrong is when capturing the video in the first place. If it's captured using a 720x480 frame with a 4:3 aspect ratio instead of ITU, and transferred to a 720x480 DVD frame, then obviously ITU resizing on playback would be incorrect. Or if it's captured with a 704x480 frame or a 720x480 frame with padding, once again if it's captured using an exact 4:3 aspect ratio, ITU resizing on playback would be incorrect. But maybe I'm missing the point completely.

Mind you I'm fairly convinced sometimes (probably more when it comes to fairly old DVDs) the aspect ratio when resizing isn't exactly correct no matter which way you do it. I'm also sure there's DVDs (mainly older ones again) which have sections using one pixel aspect ratio and sections using another and/or sections which just aren't quite right either way. And what about those DVDs which don't seem to follow any padding rule? I've got some old DVDs of TV shows where there's sections (outdoor scenes for example) where there's only something like 688x480 of picture area, or to add to the confusion there might be 12 pixels of padding on one side and around 30 on the other.

If you're a real stickler for aspect ratios you'll examine the video yourself and see which PAR should be used when you rip the DVD. But nobody can see the ~1% the difference without measuring an object with known aspect ratio on the screen. If you're using an analog CRT the TV's aspect ratio error is probably larger than 1 percent so you won't get an accurate measurement. On a computer you can count the pixels across the width and height (obviously, any image editor can do the counting for you).

I have done that before, hence my conclusion pixel aspect ratio for older DVDs is often not correct using either resizing method. I've found a straight-on shot of a round object, saved it as an image, then used an image program to draw a perfect circle around it to see which resizing method makes it round (it also eliminates any monitor inaccuracies). I've not done it much (only if I decide to really care for some reason) but even then I've sometimes thought the correct resizing would be somewhere between 4:3 and ITU.

The DVD spec does have a mechanism by which ITU PAR could be specified, the Sequence Display Extension. So a 720x480 ITU frame could be used and the Sequence Display Extension could indicate that the 4:3 or 16:9 DAR picture is contained in the inner 704x480 sub frame. But I've never seen this on a commercial DVD. The only time I've seen it used is when the DVD is flagged 4:3 DAR and the Sequence Display Extension specifies a 540x480 sub frame contains that DAR. Which means the full 720x480 frame is 16:9 DAR.

I recall reading about the Sequence Display Extension a long time ago, wondering why it's never used on DVDs, and then decoding not to think about it again.

For the record.... it'd never occurred to me to look until now.... I still had some 4:3 vob files on my hard drive I'd re-encoded, so I remuxed one with MKVMergeGUI. I didn't specify an aspect ratio. It remuxed it while setting the aspect ratio to exactly 4:3. Best as I can tell, tsmuxer does the same thing, but I'm not sure how to check ts files exactly. MPC-HC displays the aspect ratio as being exactly 4:3, but I'm not sure if like the original vob file, that's just how it resizes it.

[jagabo]

Given the official DVD resizing method is slightly wider than 4:3

No, the official resizing method for DVD is to resize the 720x480 frame to exactly 4:3 DAR. Writing the ITU captured 720x480 video (where the 4:3 DAR is in a 704x480 sub frame) directly to DVD will result in an aspect ratio error upon display because the full frame, not the 704x480 sub frame, will be displayed 4:3.

To state it more simply, with 4:3 DVD, the DVD player should display the 720x480 frame as 1.33:1 DAR. An ITU captured video with a 720x480 frame should be displayed 1.36:1 DAR.

[hello_hello]

No, the official resizing method for DVD is to resize the 720x480 frame to exactly 4:3 DAR..

I'll take your word for it, but I'd always been under the impression DVDs were supposed to be resized to the slighter wider than 4:3 or 16:9 aspect ratio, or ITU aspect ratio. That's certainly changed my view of the world.....

[jagabo]

No, the official resizing method for DVD is to resize the 720x480 frame to exactly 4:3 DAR..

I'll take your word for it, but I'd always been under the impression DVDs were supposed to be resized to the slighter wider than 4:3 or 16:9 aspect ratio, or ITU aspect ratio. That's certainly changed my view of the world.....

The official DVD spec is hard to come by. I have not seen it posted online. To get a copy you need to pay a few thousand dollars. Somebody who had a copy indicated that the references to aspect ratio referred to the MPEG 2 spec. I took his word for it. The MPEG 2 spec is pretty clear: the full frame comprises the DAR, except in the case where a Sequence Display Extension indicates otherwise.

http://cutebugs.net/files/mpeg-drafts/is138182.pdf



I suppose there is some wiggle room here. This is a preliminary document. I haven't been able to find the final document online. What is the exact meaning of "the entire active region of the display"? Could it include the front and back porch (the area outside the 704x480 ITU spec) in an analog signal?