[HELP] How do I change the display aspect ratio?

[DannyHicks]

I wanted to resize a 720x480 video (from an NTSC DVD) to 720x576, to make it match my PAL DVD video footage.

So I went to Crop/Resize, enabled Resize, and I set the Target resolution to 720x576. 

The result looked a little weird. Stretched vertically. It makes sense, considering I increased the height. I realised that my 720x576 footage is shown in video players as if it's 768x576. In my video player I found this "display aspect ratio" value that said 4:3. So I concluded that the problem with my converted 480p video could possibly have to do with that. 

In the Crop/Resize tab, I found Pixel Aspect Ratio (PAR), and I decided to set Input PAR to 4x3, thinking that would solve my problems. I believe the values were set to 7x8 by default.

Interestingly, the (displayed) aspect ratio of the video did change after doing this, but not in a good way. The display aspect ratio became 5:3. And the video looked horizontally stretched, with a display resolution of 960x576.

I was hoping you could help me out. Was I messing with the wrong values in Hybrid? How can I make my video 720x576 with a display resolution of 768x576?

[Selur]

I wanted to resize a 720x480 video (from an NTSC DVD) to 720x576, to make it match my PAL DVD video footage.

• Read [INFO] About pixel aspect ratios,.. Ideally you also read the linked websites if you don't understand the connection between display and pixel aspect ratio. Since you clearly lack in understanding the difference between PAR and DAR.
  
• load your content
  
• Open Vapoursynth Preview, if your content was properly flagged the preview should look correct.
  
• If the content is no not displayed correctly adjust 'Crop/Resize->Base->Pixel Aspect Ratio (PAR)->Input PAR' until it does.
  
• Properly crop all black bars using 'Crop/Resize->Base->Picture Crop'
  
• Enable 'Crop/Resize->Base->Pixel Aspect Ratio (PAR)->Convert output PAR to' and set it to 'MPEG-2 PAR 4:3 (16/15)' or 'MPEG-2 PAL 16:9 (64/45)' depending on your PAL DVD.
  
• Set 'Crop/Resize->Base->Picture Resize->Target resolution->width' to 720.
  
• Enable 'Crop/Resize->Base->Letterbox' and set Width to 720 and Height 576.
  

This would be the way you convert NTSC to PAL for DVD content while maintaining a proper PAR and get the proper DAR (display aspect ratio).

Cu Selur

[DannyHicks]

Thanks!

I wanted to reply on the thread you linked because I wanted to ask something about it, but it seems like the ability to reply is disabled there, so I'll ask it here.

If I understand it correctly, PAR is the width and height of each pixel, SAR is the width and height of the source video without PAR applied, a.k.a. if the video used a PAR of 1:1, and DAR is the result of displaying the video with the intended resolution.

Is PAR a thing for image files? I suppose not?

I noticed that when I make a snapshot of a PAL DVD video that's playing in media player MPC-HC, where the displayed resolution was 768x576, the saved snapshot would be 720x576. I assume this is the "storage resolution". However, when I take a snapshot in VLC, I actually do end up with a 768x576 image. Since this second snapshot does in fact have a greater width and doesn't seem to have a different PAR, I assume this image, while staying truthful to the DAR, will have some quality loss, since it's basically resized from the storage resolution.

[Selur]

Is PAR a thing for image files? I suppose not?

PAR usually only is used in combination with video.

I noticed that when I make a snapshot of a PAL DVD video that's playing in media player MPC-HC, where the displayed resolution was 768x576, the saved snapshot would be 720x576. I assume this is the "storage resolution". However, when I take a snapshot in VLC, I actually do end up with a 768x576 image. Since this second snapshot does in fact have a greater width and doesn't seem to have a different PAR, I assume this image, while staying truthful to the DAR, will have some quality loss, since it's basically resized from the storage resolution.

Sounds, right, one is making an image of the raw data it got and the other is taking an image of the data it presents to the user.

[DannyHicks]

Ah, that's pretty interesting then. 

I also just realised that taking a snapshot of some PAL DVD with 16:9 footage also returns a 720x576 image, which looks relatively even more squished than 768x576 footage in 720x576.

I guess this is how (PAL) DVDs are able to support widescreen. They don't add more pixels but they squish the footage to 720x576 and then play with the DAR and make it 16:9 instead of 4:3.

And I guess this also explains why 16:9 footage looks worse in quality, a bit blurry, because they're stretching the PAR more.

[Selur]

You have to keep in mind why anamorph conten was added.
in short: you got a restricted amounts of resolution you can transmit/store i.e. 720x480 or 720x576 (DVD resolutions, but was also true for VCD and SVCD resolution), your content does not have that resolution.
So you can either: shrink your content to fill the resolution in one dimentsion and add black bars or squish or stretch it to fit the given resolution.
-> Using anamorph encoding makes sense (when resolution is restricted due to a standard or physical restriction) and usually should deliver better quality than the alternative, unless the resized used to get the image to square pixeln is bad.

Cu Selur