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Old 4th September 2013, 14:54   #1  |  Link
Xoemab
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Is Aspect Ratio Error very important?

So i have video source that is 640x480, i cut 4 from the left and -12 from the right now is 624x480 and Aspect Ratio Error is -0.28409. I tried to resize to smaller size so the ratio go back to 0 and I found 352x270. So its better to resize to this resolution or leave it with the above aspect ratio error?
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Old 4th September 2013, 15:04   #2  |  Link
LoRd_MuldeR
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Cropping doesn't cause any aspect ratio "error", but it may change the aspect ratio.

Your original 640x480 sources was 4:3 (assuming a PAR of 1:1). Now, after the cropping, you got 624x480, which is 4:3.08. There's nothing wrong with that. It's just a slightly different aspect ratio.

Now, if you view the result on a 4:3 screen, you may see some tiny "black borders". To avoid that, you could resize the cropped video to exactly 4:3 again. But then you get some error!

And since pretty much every screen is 16:9 nowadays, you get huge "black borders" for 4:3 content anyway. Thus, the difference between 4:3 and 4:3.08 shouldn't matter at all on a 16:9 screen.
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Last edited by LoRd_MuldeR; 4th September 2013 at 15:09.
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Old 4th September 2013, 15:16   #3  |  Link
Xoemab
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So its bug of megui that when i cropping it changing aspect ratio error? And the cropping will not affect my encoding quality at all? I saw some guys that were resizing their videos i thought that was the reason.
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Old 4th September 2013, 15:31   #4  |  Link
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Quote:
Originally Posted by Xoemab View Post
So its bug of megui that when i cropping it changing aspect ratio error?
Cropping can change the aspect ratio. That's inherent in the nature of cropping. But, as opposed to changing the aspect ratio via resizing, cropping does not deform the content.

I don't know what you or MeGUI considers as "error" here. And with respect to what. Maybe you should make that clear first...

Quote:
Originally Posted by Xoemab View Post
And the cropping will not affect my encoding quality at all? I saw some guys that were resizing their videos i thought that was the reason.
With cropping you are removing pixels, so it actually becomes easier to encode (at the same bitrate), which should result in better quality (if it makes a difference at all).
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Last edited by LoRd_MuldeR; 4th September 2013 at 15:36.
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Old 4th September 2013, 15:34   #5  |  Link
Xoemab
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Thank you very much!!
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Old 4th September 2013, 20:25   #6  |  Link
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Quote:
Originally Posted by Xoemab View Post
So its bug of megui that when i cropping it changing aspect ratio error? And the cropping will not affect my encoding quality at all? I saw some guys that were resizing their videos i thought that was the reason.
If MeGUI is showing an aspect ratio error, then there'll be one.
If you crop without enabling resizing, the remaining video will be encoded "as-is". The aspect ratio of the "remaining" picture won't change. Well the display aspect ratio will, as LoRd_MuldeR explained, but the shape of objects within the remaining video won't be distorted. That's assuming the input video uses square pixels.....

What "may" have happened.....
I'd assume a 640x480 video would use square pixels and be 4:3, but it's possible the video had a slightly different display aspect ratio than 4:3 (resolution and display aspect ratio aren't always the same). So if you resize it back to 640x480's worth of square pixels, that will distort the picture.
When you set up an encode, the script creator should display the aspect ratio of the source video accurately in the InputDAR section. Is it 4:3?

If the source video doesn't use square pixels, I'm pretty sure MeGUI will display an aspect error as soon as you open it. In order to fix that you'd either need to enable anamorphic encoding (encoding using the same shape pixels as the original) or without anamorphic encoding enabled, you'd need to use resizing and/or cropping to resize it to square pixels and get the aspect ratio distortion as close to zero as you can.

A -0.28409% aspect error is fairly small. Less than 1/3rd of a percent. Even aspect ratio distortions of 2 or 3 percent can be pretty hard to pick unless you can directly compare it to the original video.

Last edited by hello_hello; 4th September 2013 at 20:28.
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