Avisynth MPEG2Source aspect ratio

[Megafox]

Why does VirtualDub display video with a resolution of 720x480 (4: 3), when in fact it should be 640x480 (4: 3)? I checked the d2v file, changed the resolution with the text editor, but it did not help.

[sneaker]

720:480 ist neither 4:3 nor 16:9. DVDs are anamorphic. The player resizes the picture on playback.

720/480 = 1.5
4/3 = 1.333333....
16/9 = 1.777777....

Search forum about anamorphic.

[lordsmurf]

720x480 is SAR, not DAR.
storage vs display.

Rectangle pixels, not square.

[_Al_]

Think of anamorphic video as video with any resolution , but simply embeding SAR into stream, in this case 8:9 and that SAR tells player what the DAR is, Display Aspect Ratio

For example you play that video in a window that has exactly 480 lines, so that player calculates 720 * 8/9=640. And that goes on your screen, 640x480.

Or you play it full screen, you have fullHD monitor, 1920x1080 resolution, so it draws 1080 vertical lines (stretches vertical 480 points into 1080, 1080/480=2.25). So it calculates horizontal resolution again 720 * 8/9 , but adding that stretch 2.25, so you get 720 * 8/9 * 2.25 = 1440

so you see 1440x1080 and player adds black borders left and right to fill to 1920

This is what players do, adjusting , calculating after every time you manually re-adjust your player window.

[jagabo]

Why does VirtualDub display video with a resolution of 720x480 (4: 3)

Because what's in the MPG file is 720x480, with a flag telling the player to display it as 4:3. Mpeg2Source() and AviSynth don't care about DAR flags. They give you what's actually in the file, pixel-for-pixel. Which is exactly what you want while editing.

[_Al_]

ok its a mpeg file , sorry, no SAR in the stream

[_Al_]

.....

[Megafox]

What are the ways to make the pixels square? Static resolution of 640x480 without stretching. Other container?

[LMotlow]

Right-click on either the VirtualDub input or output window to get a menu for displaying at different aspect ratios. You can do the same thing with your media players using their playback menus.

[sneaker]

What are the ways to make the pixels square? Static resolution of 640x480 without stretching. Other container?

Three options:
1. resize to 720x528 (square pixels upscaled)
2. resize to 654x480 (square pixels downscaled, not recommended)
3. encode at 720x480 but flag stream so player knows it has to resize (x264/x265 --sar 10:11)


[Attachment 44620 - Click to enlarge]

(If you have black bars you want to crop target resolutions become slightly different, but sar is always the same because it's the ratio of a single pixel.)

[jagabo]

If you're wondering why people are giving different values for the sampling aspect ratio (aka pixel aspect ratio), and different sizes to scale to, it's because there are two conflicting specifications. The MPEG 2 spec clearly states the full 720x480 frame contains the 4:3 image. But the ITU rec.601 spec for analog video capture puts the 4:3 image in a ~704x480 frame -- typically extra pixels at the left and right of the frame are captured in case the broadcast or cap is off center, resulting in a 720x480 frame. So a 720x480 ITU cap is slightly wider than 16:9. When making DVDs the difference between these two specs is usually ignored. 720x480 ITU caps are written to DVD without compensating for the difference between the specs.

[manono]

What are the ways to make the pixels square? Static resolution of 640x480 without stretching. Other container?

You're using AviSynth so you're going to reencode anyway. Just add lines to the script to crop and/or resize. Not hard.

Why does VirtualDub display video with a resolution of 720x480 (4: 3), when in fact it should be 640x480 (4: 3)?

No, it shouldn't.