Quantcast Aspect Ratios when editing - What is AR, DAR, SAR ? - digitalFAQ Forum
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  #1  
03-27-2010, 01:08 AM
Kereellis Kereellis is offline
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I'm still left wondering what to do about the PAR settings in Premiere though. I do all my captures in 720x576, which isn't 4:3 per default, and I assume the pixel ratio of these caps is square, since overriding the default aspect ratio in MPC results in a stretched horizontal dimension compared to the original. Does this mean that if I normally play back my captures on pc, I'm actually watching a slightly elongated version of the original material?

Would it in that case be better to archive my captures as is or should I change the PAR somewhere in the compression procedure for a more correct AR on playback? I'm hesitative about it since I expect changing the PAR to somewhat blur the image like MPC, and then I might as well stretch the original video upon playback if I need to.

Also, why is it that neither of my capture devices (neither the easycap nor the ATI) support 768x576 if that matches the default ratio for PAL? Do they already capture non-square in the right PAR or am I right in assuming they just capture square pixels in the wrong aspect ratio?

Finally are there any misunderstandings that show from my reasoning? I actually never got into the whole PAR subject before this, and it's hard to find some clear answers about PAL VHS sources and capturing regarding the matter, so I'm mostly left guessing.
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  #2  
03-27-2010, 02:15 PM
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PAL and NTSC video is stored in non-square pixels.

DAR = display aspect ratio, often referred to simply as "aspect ratio" (or "AR")

SAR = storage aspect ratio, and is not often mentioned or talked about. 720x480 (NTSC), for example, is 3:2 aspect. However, you'll never watch it this way. 352x480 is something like 11:20 aspect. I forget the PAL SAR's, don't know them offhand, because I work more with NTSC and have those memorized. This information is only useful in certain scenarios. For example, when you want to crop off pixels in a non-4x3 editor (VirtualDub's crop feature), but maintain final aspect (both SAR and DAR).

The two generally have no overlap.

720x576 = 4:3 AR (DAR), and something else for SAR
720x480 = 4:3 AR (DAR), and 3:2 SAR
352x576 = 4:3 AR (DAR), and something else for SAR
352x480 = 4:3 AR (DAR), and 11:20 SAR

... same for 352x240, 352x288, 704x576, 704x480, 480x480, 480x576, etc

You'll see SAR when you use 1:1 square pixels. But that's not proper NTSC or PAL video encoding -- that's non-format video sizing.

640x480 = 4x3 @ 1:1 square pixels
320x240 = 4x3 @ 1:1 square pixels
... and there are MANY more possible combos. Just pick a number a and multiple it by 4 and by 3, and it will be a valid size where both are divisible by 8.

Just remember that the pixels of video data for NTSC and PAL video are not square.
  • Good computer player software will show the pixels properly.
  • Bad computer player software will squish/stretch the video in odd ways, forcing the rectangle-shaped pixels into improper little squares.
  • Editors can vary in how their preview works, so pay attention to aspect settings when setting up a project, or when viewing the preview windows. (In VirtualDub, for example, you can right-click the preview to show it 4:3. In Premiere, you set up the project to have proper AR.)
That's really all there is to it.

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03-27-2010, 02:20 PM
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I also noticed you've used "PAR" a few times.
  • If PAR = "picture aspect ratio", then PAR = DAR = AR, and PAR=DAR because you only see picture when it's displayed.
  • If PAR = "PAL aspect ratio", then there is no such term. PAL is not inclusive to the topic of AR, but there are PAL version AR/DAR and SAR
... I'm starting realize when I hate tech jargon again. I feel like I'm speaking Klingon. "Par, sar, ar, tar, gar!"

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03-27-2010, 03:50 PM
Kereellis Kereellis is offline
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PAR stands for 'pixel aspect ratio'. It's the term used in Adobe Premiere for this setting. For Pal video this is 1.067:1 according to Premiere (actually it's probably rounded up from 1.066666 etc.).
Thankfully this would make sense to me since 1.067x720 = 768 and 768:576 = 4:3.

I had also noticed now that upon explicitely selecting 'square pixels' instead of 1,067 PAR for the export settings, the resulting image was flattened (I would expect elongated, but for some reason the vertical resolution was lessened in MPC..). However this may only have been the case since this time I had the PAR value set to 1,067 in the project settings as well. That is to say, I remember selecting square pixels for both the project and export during my first conversion attempt, and the exported clip retained it's original 'DAR', as the Klingons would say.

Anyway, am I right to conclude from your explanation that the SAR for 720x576 = 5:4?
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03-27-2010, 04:38 PM
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Yes, 5:4 sounds correct for 720x576 PAL. That's it.

Even I'm a bit confused by the use of "pixel aspect ratio". I guess that's the Adobe way of trying to distinguish between square and rectangular pixels at a micro level (pixels) instead of the macro level (full sized video image). I would imagine that PAR = DAR = AR, in this case.

I think I'm getting a headache now.

Quote:
1.067x720 = 768 and 768:576 = 4:3.
The math is correct, yes.

Quote:
Thankfully this would make sense to me
This is the most important part, of course.

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  #6  
10-26-2019, 01:26 PM
SFtheGreat SFtheGreat is offline
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Quote:
Originally Posted by Kereellis View Post
For Pal video this is 1.067:1 according to Premiere (actually it's probably rounded up from 1.066666 etc.).
Thankfully this would make sense to me since 1.067x720 = 768 and 768:576 = 4:3.
And this is plain wrong. The PAL PAR is 1,094 for 4:3.
https://www.mikeafford.com/blog/pal-...ts-cs4-vs-cs3/

Last edited by SFtheGreat; 10-26-2019 at 02:08 PM.
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