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Old 26th August 2009, 07:15   #1  |  Link
an3k
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Why does DivX uses wrong PAR? / How SAR/PAR/DAR is correctly calculated

Hi everybody,

first i would like to explain SAR, PAR and DAR. I often read that PAR belongs to the Pixel Aspect Ratio of the Screen i want to use but this is completely wrong. It has nothing to do with the Display you use to watch a movie. No difference between PC-Monitor or Television!!

Lets begin:
SAR = Storage Aspect Ratio
PAR = Pixel Aspect Ratio
DAR = Display Aspect Ratio

SAR is calculated by Width divided by Height (eg. 1920/1080 = 1,7777777777777777777777777777778 which is rounded to 1,778 which is 16:9), thus SAR only specifies in which Aspect Ratio the Video is saved. Period.

DAR is the Aspect Ratio you want your video to be shown in. For example if you create a video with SAR of 1,250 (5:4 or eg. 720x576) and want it to be shown as 16:9 you have to set the DAR to 1,778 (16:9).

PAR is used to calculate the correct DAR by using the SAR.

Example:
We have a video with a resolution of 720x576, the PAR is 5:4 or 1,250. We want to show it in 16:9 or 1,778.

We only need two information to get the third. If we have SAR and DAR we just do DAR / SAR = PAR

If we have SAR (we always have this information) and PAR we just do SAR * PAR = DAR. This is what PC-Software, TFT-TV-Screens, DVD-Players, etc. do.

Open a DVD vob file and check the information GSpot gives you. You see that for the example above the PAR must be 1,422 but in Divx we only can set useless values like 16:11 = 1,455 (16:9 PAL) and 40:33 = 1,212 (16:9 NTSC). If DivX would change this we could create anamorph DivX.

I hope you understand what i wrote and can answer my question: Why does DivX uses such useless values?

@ DivX Developers: Just remove the "Input format" and "Output format" inputs and create a single one in which the user can enter a value like 1,422 or 1,066 (no dropdown!! manual input by user!!) and everything will be fine. The info in this field should be passed directly into the video, no need for the encoder to modify it. Thank you!

I always had my problems with those stuff but after i took a accurate look into GSpot i knew how it works. Yes, GSpot gave me all of that information.

Last edited by an3k; 26th August 2009 at 07:29.
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