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Old 08-27-2014, 02:49 PM   #1
J4ZZ
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Default [Guide] Aspect Ratio | PAR SAR DAR FAR

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 720480. 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 720480 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
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Last edited by J4ZZ; 06-18-2017 at 12:20 AM..
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Old 08-29-2014, 10:01 AM   #2
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Default

Additional (and more technical) info can be found on wikepedia :

https://en.wikipedia.org/wiki/Pixel_aspect_ratio

https://en.wikipedia.org/wiki/Display_resolution

https://en.wikipedia.org/wiki/Overscan
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Old 09-06-2014, 11:53 PM   #3
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Default

i don't have a problem understanding aspect ratio or resetting a player when a vid defaults to something it obvious ISN'T, but...isn't there a way to get this info packaged WITH the vid? why shud i, a HUMAN (they say), have to realize by sight that it's set wrong?

worse yet, even after adjusting the setting in a player, it goes BACK to the default once u hit stop! ugh. even with the vid still loaded there.

i've learned the hard way to pull the slider back to zero, rather than hitting stop/start as i normally would.

this is really a pain.

VLC and WMP mostly.
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Old 09-07-2014, 05:37 PM   #4
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Default

This is called "Anamorphic Encoding" where the encoded aspect ratio (AR) of a movie is different from the displayed aspect ratio.

You can set this information in mkv, mp4 and technically even in avi files.

So, what is it exactly.

Well, basically it's simply putting the Display Aspect Ratio information into the video file like it's done on a DVD (store in one aspect and display in another).

There are two prefered methods to choose from. Strict and Loose anamorphic

Strict anamorphic concentrates only on one thing: preserving the exact visible frame of a DVD, displayed to exactly the same size as it would be from the DVD.
This means it will sometimes use odd dimensions, ones that don't divide cleanly by 16. When this happens, the video encoders cannot work as efficiently — x264 warns that "compression will suffer."
It also means that, when using strict anamorphic, it is impossible to change the stored size of the encoded frame. It will simply use the exact frame size of the DVD and apply cropping.

Loose anamorphic starts off the same way as strict -- with the exact visible frame on the DVD. But then it adjusts the dimensions to be sure they divide cleanly by 16. After that, it adjusts the display size so the film's aspect ratio is preserved with the new dimensions.

MeGui, Handbrake, Vidcoder and many others are capable to add this information when encoding.

If you need to change AR in existing mp4 or mkv files without re-encoding you could use mp4box (yamb is the gui) or MKVmerge (part of the MKVToolnix package). For avi files there is MPEG4 Modifier for getting the job done.

Regards,

J4ZZ
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Old 09-08-2014, 03:22 AM   #5
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Default

Always much simpler, if the person that originally does the encoding of
a transfer/dvdrip, sets the aspect ration correctly to begin with. The
easiest way to determine what the correct aspect ratio from a DVD,
would be to simply look on the back of the DVD box that it came in,
where that info is given almost always. VHS tape Laserdisc transfers,
are even simpler. Without exception, they're always 4:3.

Any movie or video that I download from someone else, that I plan on
keeping for myself, is always corrected with another encode, and the
original out of kilter video thrown away.

The below site, is great in helping one determine the resolutions for
any particular video one has, as well as the resolutions that one needs
to get to, to do a re-encode to get it to the correct aspect ratio.....

http://www.digitalrebellion.com/weba...pect_calc.html


Of course one won't always have a dvd box to see what the aspect
ratio is that the video is supposed to be, but for anything with a listing
at IMDB, that aspect ratio can be found in the listings "technical" data.
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Old 03-21-2015, 10:47 AM   #6
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Default Film Aspect Ratios

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Thanks and credits to the original uploader
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