[Guide] Aspect Ratio | PAR SAR DAR FAR

[J4ZZ]

Since there are more and more rips with a borked aspect ratio (AR) I'll try to shed some light upon this topic.

There are two main ways of describing aspect ratio - Pixel Aspect Ratio (PAR) and Display Aspect Ratio (DAR).

Explanation:

A pixel is a pixel, it is a small block of color information. However, some playback devices have different shaped pixels than others. Computer monitors have square pixels and hence everything that is designed for display on a monitor should have a PAR of 1. TVs however have 'rectangular pixels' which have a different PAR depending on the format (NTSC or PAL).
The thing is that most of our classics were supposed be shown on a 4:3 TV back then. But when transfered to DVD the storage resolution changes to fit a DVD compliant shape. So this is what we basically have to correct when making a rip for a digital display with a pixel aspect of 1 (sqare pixels).

But why the weird ratio on a DVD at all? (Explained for a NTSC DVD)

There's a good reason for it. DVD was designed to perform well with both 1.33:1 (4:3 television) and 1.78:1 (16:9 widescreen). But instead of having two different pixel resolutions, (NTSC) DVD uses only 720×480. Since 1.5:1 is about halfway between 1.33:1 and 1.78:1.
Let's call this the Storage Aspect Ratio (SAR) or the Frame Aspect Ratio (FAR)

"Full screen" 4:3 video

To achieve this, videos are first squished or stretched to fit into 720×480 pixels. Each video is marked with a bit of information telling the DVD player whether 4:3 or 16:9 should be used for playback. The DVD player then automatically does the appropriate squishing or stretching to restore the proportions to normal.

The same concept applies to PAL but with 720x576 pixels.


So here are two simplified rules for 4:3 content on DVD

NTSC: storage resolution is 720x480 but display resolution is 640x480
(so downsizing to 640x480 is needed for the movie to look right on a PC monitor)

PAL: storage resolution is 720x576 but display resolution is 768x576
(so upsizing to 768x576 is needed for the movie to look right on a PC monitor)

See image for an (exaggerated) illustration:



Now finally, if you have a DVD ripped to your harddrive and want to know what the actual display resolution is, you can simply check by dropping the VIDEO_TS folder into Vidcoder for example and then have a look at the Settings -> Picture - Input-bubble...



That's it basically...

Feel free to add more infos and/or give comments.


Regards,

J4ZZ