DVD Authoring & Aspect Ratios

[hizzy7]

Hi Video Jedis!

I have a question about DVD Authoring & Aspect Ratios. I have been fixing up videos in Virtualdub with Avisynth. For my work flow, I often create a lossless AVI in VDUB, and then I load that AVI into programs that allow me to edit the video as needed. When I have a DVD that 16:9, VDUB creates an AVI that is 4:3. My understanding is that AVI doesn't really have a way of specifying the display aspect ratio, and so you have to manually set the AR in a player like VLC to see the film display at your desired AR. My question is: When authoring for DVD, should I re-size the video that I create in VDUB to display how I want it to, or should I leave the AVI alone and, when authoring the DVD, set flags to display at the correct aspect ratio?

Thanks!!

h

[El Heggunte]

Please read again:

https://www.videohelp.com/dvd#tech

because what you wrote doesn't make much sense. Also, VirtualDub basically does what the user tells it to do, so I don't see how it "creates 4:3 videos" «against your will»

FWIW: according to Alexander Noe:

The Open-DML AVI standard includes a VIDEOPROPERTYHEADER for video streams, which allows to indicate the output resolution in the sense of Matroska's DisplayWidth and DisplayHeight elements.

The problem is that DirectShow does not read those values (at least the DirectShow documentation does not mention support for this feature). MPEG4 has an aspect ratio stored in the bitstream as well, and ffdshow as well as a few other decoders use this aspect ratio, raising the wrong impression that anamorphically encodec video would properly work in AVI. But truth is, AVI is as unsuitable for anamorphically encoded video as OGM.

[hizzy7]

Hmm...

Perhaps I am mistaken somewhere. AR befuddles me. Would it make more sense if I said that it takes a 4:3 display and makes it 3:2?

[Cornucopia]

Here's what you need to remember about ARs:

Display, or Frame, Aspect ratio is all about the total, combined image (and how it fits? the screen).
Pixel, or Sample, Aspect ratio is all about each individual pixel/sample (and how it makes up the image).
The 3rd kind of AR (Storage AR) is only a ratio for those who don't understand that the dimensions of the image stand alone. It is only pertinent when dealing strictly with non-anamorphic square pixels.
Also,
Most containers DO designate one of those 2 (but never the 3rd) ARs. AVI is an exception, although it is possible to use certain flags in that capacity (but it would be non-standard). However, even with AVI, many elementary video streams use codecs that have AR designation features. So, for example, an AVI that contains h264 video may not have AR info on the container level, but it DOES have AR info on the coded video stream level.

Next, you should know that really the only app sections that actually matter to the AR of the footage are the encoders & decoders. AVISynth in particular (because it is a frameserver) and Virtualdub, by extension, do NOT support or understand ARs (only the 2 dimensions' resolutions) - it must be defined elsewhere.

HCEnc (MPEG2), Xvid (Mpeg4ASP), x264 (Mpeg4v10/AVC/h264), etc. are what you need to concentrate on re: the AR.

Clear as mud, right?

Scott

[hizzy7]

Hi!

Because it is best to provide as exact info as I can, I wrote down the info I see from mediainfo

The original DVD is 720*480 (16:9)

My lagarith AVI is 720*480 (4:3)

Is there no Storage AR for lagarith?

Should I re-size the lagarith video or "define" the AR with a flag?

Thanks! Sorry that I am so dense :P

[newpball]

Hi!

Because it is best to provide as exact info as I can, I wrote down the info I see from mediainfo

The original DVD is 720*480 (16:9)

My lagarith AVI is 720*480 (4:3)

Is there no Storage AR for lagarith?

Should I re-size the lagarith video or "define" the AR with a flag?

Nope, only when you transcode to a delivery codec you need to indicate the AR.

[davexnet]

Yes. Problem is, the Lagarith video being 720/480 is 3/2. It may be interpreted incorrectly when it is encoded to DVD.

AVStoDVD has a feature that is useful in cases like this. It is possible to override the source A/R in the project.

[hizzy7]

Could I use something like ifoedit to put a flag to display at 16:9? Is that better than re-sizing my lagarith avi?

Thank you!

[LMotlow]

Hi!

Because it is best to provide as exact info as I can, I wrote down the info I see from mediainfo

The original DVD is 720*480 (16:9)

My lagarith AVI is 720*480 (4:3)

Is there no Storage AR for lagarith?

Your Lagarith AVI is decoded video in a lossles AVI container, which has no "display" aspect ratio. In square pixels (which is what your computer is using) 720*480 has a physical aspect ratio of 3:2 (can also be stated as 1.5:1). Because the AVi has no display aspect ratio flag (or it shouldn't, unless you did something weird), its physical aspect ratio and its display aspect ratio are the same.

I have no idea where you get 4:3 for a decoded lossless 720*480 AVI compressed with Lagarith.

With some encoding apps, when you input a video the app will often show an aspect ratio that's really a "guess", or default. When you encode your 720x480 AVI to MPEG2 for DVD, you must specify to the encoder whether the display aspect ratio is to be 16:9 or 4:3.

Should I re-size the lagarith video or "define" the AR with a flag?

Resize to what ? Your DVD frame size has to be one of the frame sizes shown in the DVD tech link that was posted earlier. 720X480 is the most common size for DVD video that will display at 16:9.

[davexnet]

Use AVStoDVD, indicate the *real* aspect ratio of the source and create your DVD.
This is done by right clicking the file in the project window and selecting "edit source title
info/video display aspect ratio" - enter 1.333.

[hizzy7]

LMotlow, you are right!! It is 3:2. Sorry, it is late where I am. Late night typos :P

[_Al_]

One thing that helps to realize how it works,..., DVD has the same resolution 720x480 for 4:3 and 16:9 video, so you must specify aspect ration in DVD authoring. Whatever DVD authoring you use, you have to make sure to set it correctly, obviously that information cannot be pulled from avi container with lossless video in it even if that DVD authoring was attempting to do that automatically.

[newpball]

This is done by right clicking the file in the project window and selecting "edit source title
info/video display aspect ratio" - enter 1.333.

No.

The source is widescreen, widescreen is 16:9

[davexnet]

This is done by right clicking the file in the project window and selecting "edit source title
info/video display aspect ratio" - enter 1.333.

No.

The source is widescreen, widescreen is 16:9

OK. If the OP mentioned somewhere above the source was really 16/9 I missed it.
In that case, if you're going to try AVStoDVD, enter 1.777 as the A/R.

[hizzy7]

Does AVStoDVD add a display flag or does it re-size, or is there even a difference?

Thank you!!

[_Al_]

To resize proper DVD resolution 720x480? Most certainly not. It would make no sense.

[manono]

...so you must specify aspect ration in DVD authoring. Whatever DVD authoring you use, you have to make sure to set it correctly...

Would it not be more accurate to say you set the DAR when encoding? The authoring programs with which I'm familiar will author the video as it was encoded and you'd have to consciously change it if you wanted something different.

Authoring is a completely different operation from encoding, even if some programs do both. Maybe some all-in-ones (AvsToDVD?) will have you choose both at the same time. But, for example, after encoding a video as 16:9 in my MPEG-2 encoder it'll automatically be authored as a 16:9 DVD in Muxman or other authoring programs.

[_Al_]

yes, that's more accurate, and overall explaining of separation of encoding and authoring

[hizzy7]

I have a series of what might be very stupid questions

This may be the stupidest question, but is changing the pixel aspect ratio the same as using lancosresize?

Should you ever change the PAR of a video? Should I be setting the DAR?

When authoring a DVD, what PAR should I be aspiring to?

Thank you all for your help!!

[_Al_]

It is not that complicated as you think. Encode lossless 720x480, with no aspect ratio setting whatsever.

Then scenario
1) you encode it with 16:9 aspect ratio and import into DVD authoring, setting project as 16:9 perhaps, setting 16:9 flag somewhere for video

2) you import that lossless into DVD authoring and setting it to 16:9, perhaps you need to set project as 16:9 and video as well as 16:9, that yo set for mpeg2 encoder or somewhere in the menu etc, it could differ software from software. Maybe some software does not need to set it, because assumes 16:9 video as output anyway loading it into 16:9 project etc

So it loos the same anyway, Not sure why you talk about resizing here all the time, there is no resize, your lossless is 720x480, that is good.

[hizzy7]

Hi!

The re-sizing became a question for me when I noticed the lossless avi that I created was not displaying the same way as the DVD it was taken from. The DVD always looked normal, but the AVI looked squished and there are black bars to right & left which were absent from the DVD. That made me think that a) I should be doing something like a re-size when making my AVI to have it display correctly; or b) that there was a step in the encoding process that would make the my resulting video display correctly. I found that when I changed the PAR in my encoder that the picture then looked perfect, but I am confused about changing the PAR. Is changing the PAR the same as re-sizing? What does changing the PAR do a video? I can see that changing the PAR makes the video display correctly, but I am curious as to why or how that process works.

Thank you to _AI_, Manono and everyone for your advise and help! Videohelp should be called videosaviors!

[_Al_]

You can think of it this way. That aspect ratio in anamorphic video just tells player how to stretch or squeeze horizontal resolution, nothing else.

In DVD case for example you load 16:9 DVD movie into PC player in computer and that player sees ar for 16:9 video as 32/27 because it knows it is 16:9 DVD, that is specifications, so it multiplies horizontal resolution to 720x32/27=about 854 so you see on computer display video as 854x480. So those players calculate missing pixels while rendering it on screen. That player does live upscale to those 854 on screen, even if real pixel value for horizontal resolution is 720 only.

Using CRT it works differently, of course, in that case DVD player just squeezes those 480 lines into 480x27/32=about 405 lines so you get black bars above and below video. Same way works rendering in PC if you minimize window enough.

For other variants of DVD's you can read this table:
720x480 4:3, ar=8:9
720x576 4:3, ar=16:15
720x480 16:9, ar=32:27
720x576 16:9, ar=64:45

those values could differ a bit depends if we talk about certain two standards but just to give you a ballpark how it works

[hizzy7]

Hi,

So when my lagarith avi appears horizontally squished, it has not been shrunk. It is that the horizontal resolution has changed and the pixels are just displaying differently? It's the same amount of pixels, just displayed differently?

Thanks!

[_Al_]

It is the same amount of pixels displaying correctly.

They are rendered on screen as stored resolution is. 1:1. 720 pixels horizontally and 480 vertically. That container has no room for aspect ratio so it is off. But that avi is intermediate file, it is not suppose to be watched on screen and getting correct proportions. You just watch that lossless to control how it came out regardless quallity, but not because checking right proportions. You introduce aspect ratio to it again while encoding to mp4 (H.264 giving it that ar, called SAR or whatever, I mentioned above for example 32:27) or to to mpeg2, mpeg2 can carry aspect ratio as well, or while authoring DVD, where DVD authoring reads that 16:9 flag somewhere, that you provide to it that it is 16:9 video.

The only avi file that carry aspect ratio I know of is DV avi, because it is different design, it is inside of that stream.

[Cornucopia]

Once again, you (and _Al_ now) are both referring to "stored AR", even though there is NO SUCH THING. There is only stored resolution (1 horizontal and 1 vertical). You are both making this more problematic than it needs to be. You won't find ANY container or codec that includes/specifies a STORAGE AR. The sooner you disabuse yourself (selves?) of that idea, the better. The formula is

Display AR = Horizontal rez / Vertical rez * Pixel AR

@hizzy7, you are close to the right track. DVDs can be either 4:3 DAR or 16:9 DAR, even when using the same 720x480 resolution. Since you know the formula above, you can just plug in the #s when necessary. If the DVD had a 16:9 DAR using 720x480, it had a PAR of 32:27. You can choose how you want your lag or your later downstream encodes to work: either you can maintain the non-square PAR and have the player do the "correction" on playback, or you can bake in the adjustment (using a resize) so that it henceforth uses Square PAR pixels and then the player/encoder/etc. won't have to worry about it. But, if you bake it in and re-encode, you will lose a tiny amount of quality due to the interpolation.

@_Al_, yes you do seem to understand the general idea quite all right, but if you keep referring to Storage AR, you are just perpetuating the confusion over this.
Yes, you are correct in the specialness of DV. That is mainly because it is a muxed stream inside a muxed stream, whereas most standard AVIs just have simple elementary coded streams in the contained mux. This is also why there was a need for a "Type 2" DV (because apps aren't used to that level of mux complexity). But the DV mux does not contain the designation for the AR, that is incorporated in the coded video stream itself, just like many other codecs.

Scott

[LMotlow]

So when my lagarith avi appears horizontally squished, it has not been shrunk. It is that the horizontal resolution has changed and the pixels are just displaying differently? It's the same amount of pixels, just displayed differently?

mm. Kind of all over the place here. Go back a little?

I have a question about DVD Authoring & Aspect Ratios. I have been fixing up videos in Virtualdub with Avisynth. For my work flow, I often create a lossless AVI in VDUB, and then I load that AVI into programs that allow me to edit the video as needed. When I have a DVD that 16:9, VDUB creates an AVI that is 4:3.

No it doesn't. If you feed 720x480 into VirtualDub, what comes out is 720x480. VDub resizes only if you tell it to.

My understanding is that AVI doesn't really have a way of specifying the display aspect ratio, and so you have to manually set the AR in a player like VLC to see the film display at your desired AR.

True. Lossless, unecoded 720x480 AVI displays as lossless unencoded 720x480 AVI by default in most PC media players and editors. Yes, you can tell many apps to display at the desired display AR. This doesn't change the source video itself.

Just about all PC video editing apps and players display video as square pixels. There are a few things that PC monitors don't do: they don't deinterlace, and they don't interpret DAR's or PAR's. That's a job for your media players and TV playback system. Don't think that a PC monitor and a TV playback system are the same. They aren't.

When authoring for DVD, should I re-size the video that I create in VDUB to display how I want it to, or should I leave the AVI alone and, when authoring the DVD, set flags to display at the correct aspect ratio?

The latter choice is correct. As mentioned earlier, you seem to be confusing encoding with authoring. DVD authoring apps don't resize. But With some of them, you have to purposely check and set the desired output DAR. Lots of apps try to be totally "automatic" for the sake of folks who don't know squat about what they're doing. Automation can be ornery sometimes and makes incorrect assumptions. That's why you check settings. I have one authoring app thet always defaults to the last DAR I used on my PC. That's OK if I'm making another DVD with same 4:3 DAR as before, but it's a pain in the b--t if I want 16:9 this time around.

Could I use something like ifoedit to put a flag to display at 16:9? Is that better than re-sizing my lagarith avi?

Why? If your frame dimensions are up to spec and you've encoded and authored correctly, you don't have to do any of that.

is changing the pixel aspect ratio the same as using lancosresize?

No. You ought to be using a better resizer anyway. lanczos is pretty old hat these days and has annoying resizing artifacts.

Should you ever change the PAR of a video? Should I be setting the DAR?

If you're talking about your lossless AVI, no. PAR is based on encoding processes. Setting PAR data is your encoder's job. It's up to you to check that your encoder isn't making some of those unwanted assumptions I talked about.

When authoring a DVD, what PAR should I be aspiring to?

Unless you're playing with command-line apps, many encoders don't bother with PAR. Just DAR. But since you asked, I saw some PAR numbers earlier I'm not familiar with. My Adobe and TMPGenc charts tell me that the pixel aspect ratios for NTSC 720x480 are:
DAR 4:3 = PAR 10:11 (pixels defined as height greater than width)
DAR 16:9 = PAR 40:33 (pixels defined as width greater than height)
So you see how interpreting pixel shape (PAR) in two different ways can give you two different display AR's from the same square 720x480 pixels.

The re-sizing became a question for me when I noticed the lossless avi that I created was not displaying the same way as the DVD it was taken from. The DVD always looked normal, but the AVI looked squished and there are black bars to right & left which were absent from the DVD.

You just introduced a whole new can of worms. Black side bars? Do you mean that your 16:9 video has 4:3 segment imbedded in it, or do you mean that your DVD is really 4L3 DAR with a letterboxed 16:9 image inside of it? Such a video would play with side bars. If you input a 720x480 DVD directly into VDub or an editor, your 720x480 displays at that frame size. Because the pixels in a DVD video are not encoded with square-pixel flags, a wide-screen video will look squished in a square-pixel environment. If you tell your media player or VDub to display that 720x480 video at 16:9, as square pixels it will be stretched to play as 856x480.

That made me think that a) I should be doing something like a re-size when making my AVI to have it display correctly; or b) that there was a step in the encoding process that would make the my resulting video display correctly

b) is correct.

I found that when I changed the PAR in my encoder that the picture then looked perfect, but I am confused about changing the PAR. Is changing the PAR the same as re-sizing?

No. Changing the PAR doesn't physically resize anything. It just tells your player how to do it.

What does changing the PAR do a video?

The PAR is imbedded data that tells a DVD player how to display the video.

If you want to see your video in VirtualDub at the correct aspect ratio, right-click on the OuputPanel or Input Panel and choose from any of a whole bunch of DAR's. This does absolutely nothing to actually resize your input.

[_Al_]

Cornucopia
I admit a can screw up terms all the time, your presence of explaining terms and rules and norms is always relieving,....., I do not perceive term Stored Aspect Ratio as something that is stored, printed in video, it is just that value, SAR that is stored. You can interpret it in both ways. x264 developers use that term SAR, so I jump on it. If it is wrong, perhaps. And I mentioned that SAR only once above as for H264 example, trying rather to avoid even terms PAR or DAR. So PAR it is, and those rendered values on screen are DAR, what we should see.

[Cornucopia]

IIRC, the SAR referred to by MPEG4 specs (and by association, the x264 team) is Sample Aspect Ratio. This is another term for Pixel Aspect Ratio.

How they are rendered on the screen depends on the display: square-pixel (or more accurately "fixed-pixel") displays require a runtime resize, displays that can vary their pixel AR such as CRT will just vary them appropriately and the active image's DAR will accommodate.

Scott

[manono]

The re-sizing became a question for me when I noticed the lossless avi that I created was not displaying the same way as the DVD it was taken from.

It's not supposed to display the same way as the DVD does. The DVD has a DAR of 4:3 or 16:9 and your AVI doesn't. If you want it to display in the same way, then set your software player to output 4:3 or 16:9. I do that with my Lagarith AVIs when playing them in MPC-HC. You can even make it look 'normal' in VDub by right-clicking the screen and giving it a 4:3 or 16:9 'frame'.

The DVD always looked normal, but the AVI looked squished and there are black bars to right & left which were absent from the DVD.

As for the black bars in your AVI, where do you see them? When using your software player? Means nothing. In VDub? Then you screwed up. If you start with a 16:9, 720x480 DVD and make 720x480 intermediate AVIs along the way, on the way to reencoding it as a 16:9 DVD, then nowhere during the process should you be resizing.

Could I use something like ifoedit to put a flag to display at 16:9?

Why? If your frame dimensions are up to spec and you've encoded and authored correctly, you don't have to do any of that.

And if you did manage to screw up the DAR you could use IFOEdit to correct it, yes, but it's a helluva lot easier to do using PGCEdit.