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problems with calculating correct aspect ration

Discussion in 'Other video questions' started by Scree, Aug 20, 2005.

  1. Scree

    Scree Member

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    I didn't know where else to post this, so here's my problem:
    I have an Avi with the size of 608x320 px and every pixel is film information (no borders).
    I want to turn this into an anamorphic NTSC DVD (so it displays correctly on 16:9 TV sets) with a 720x480 res. Since the source is non anamorphic I can't figure out how much I should stretch the hight. (if I wanted 4:3 I would've resized it to 720 times roughly 405 and added in black borders but then the movie would appear squished on a 16:9 TV unless I use the TV's built in zoom feature, and I hate to use it)
    Maybe someone here can point me into the right direction?
     
  2. Minion

    Minion Senior member

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    Well my Calculations tell me that to resize this File to 16:9 animorphic you would resize it to 704+304 and Fill the Rest of the 720+480 with Borders....

    You can also try 704+400(4:3) or 704+368(1:1).....
     
  3. Scree

    Scree Member

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    Thanks for the reply (although the numbers I used in the end were quite a bit different.)
    I resized the film to 720x450 and added 15 pixels worth of borders on both top and bottom. Looks perfekt now on both 4:3 and 16:9 displays. (I can't really remember how I came up with the numbers thuogh)
     
  4. celtic_d

    celtic_d Regular member

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    Yep, 450 is about right if you are using the full 720 width, 448 would probably make more sense though.

    Don't know where Minion's numbers come from though. No way that the anomorphic version should have less vertical resolution.
     
  5. Scree

    Scree Member

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    448 might make more sense but then who's gonna notice the difference in the end?
    (if I were to convert the avi again I'd probably just blow it up to the entire height of 480 - not a big difference between a 1.9:1 and a 1.778:1 ratio)
     
  6. celtic_d

    celtic_d Regular member

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    That was my point. You aren't likely to notice the difference, but the encoder will and since 448 is divisible by 16 it should compress better, potentially offering better quality for the same filesize.
     
  7. Minion

    Minion Senior member

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    I got my Calculations useing the Aspect Ratio/Resolution Calculator in Gordain Knot....These Calculations are useing Pixel Aspect Ratio because all AVI Files use a Pixel Aspect Ratio of 1:1 (Accept DV) so I find I get better results If I calculate the PAR on a 1:1 Basis....


     
  8. celtic_d

    celtic_d Regular member

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    Not all avi's are 1:1 and as far as I know DVD's never are.
     
  9. Minion

    Minion Senior member

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    DVD"s aren"t AVI...I"m Talking about PAR not DAR and all Standard Microsoft AVI"s Have Square Pixels which means they are 1:1...

    AVI files do not have an Aspect ratio Flag , aspect ratio Flags are Purely a Property of Mpeg Files...It is the Aspect ratio Flag that tells your DVD player how to Display the Video as Mpeg files are displayed useing there Pixel aspect ratio not there Resolution ,The Resolution is only used so the DVD player Knows How many Pixels to Display and these Pixels are Displayed useing there Aspect ratio....

    Cheers
     
  10. celtic_d

    celtic_d Regular member

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    MPEG4 streams can have non 1:1 PAR's, this can be read no matter what container they are in, including avi.

    Also, with Open-DML avi's you can specify an output resolution, which amounts to the same thing.

    I was talking about PAR.
     
  11. Minion

    Minion Senior member

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    Here is a Quote from "VideoHelp.com" (Formerly VCDHelp.com and DVD-Rhelp.com) regarding this Subject....

    Here is a link to the whole Explanation....

    http://www.videohelp.com/forum/userguides/174200.php

    Cheers
     
    Last edited: Aug 24, 2005
  12. celtic_d

    celtic_d Regular member

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  13. Scree

    Scree Member

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    Well, seeing that the aspect ratio I went with looks pretty much perfect on my TV I guess my (and Celtic_d's) calculations were right. The result is all the proof I need here.
     
  14. Minion

    Minion Senior member

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    Well your Link didn"t Say anything I allready didn"t Say...I was Talking about "Direct Show Microsoft AVI" not "Open DML" (like DV AVI) which I allready stated does support Aspect ratio"s.....

    You are Arguing "Open DML" and I am Arguing "Direct Show"....
     

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