How can i find Original Aspect Ratio?

[therock001]

I need to know how to find the original Aspect Ratio of Movies so that i can convert them on xvid using the correct AR.

For example i need to encode "V for Vendeta" And gspot and mplayer classic gave a resolution of 720x576 (16:9) S o according to my calculations 624x358 or something like that had the least aspect error,so in the AutoGK resize option i put 624,and when i checked the resulted video file it had a res of 624x272,which is anamorphic(2.35:1).

Y did gspot and other programms identify it as 16:9 when its 2.35:1?

Cause if that's the case 624x272 has more error than other anamorphic res,so that means i have to encode it again!

[Baldrick]

A DVD with 720x576 16:9 can be anything from 1.77:1 to 2.5:1, it depends on the black borders.

AutoGK doesn't make any anamorphic divx/xvid it crops and resize to the OAR.

https://forum.videohelp.com/viewtopic.php?t=174200

[manono]

S o according to my calculations 624x358 or something like that had the least aspect error

There are a couple of things (at least) wrong with your calculations. One is that you didn't allow for cropping away of the black bars above and below the active video. Another is that AutoGK resizes to Mod16 (both height and width divisible by 16). Your 358 is only Mod2.

AutoGK is going to crop and resize to the correct AR anyway, even without your help.

Baldrick: I have a DVD in my hands right now of a classic film (The Maltese Falcon) where there's a trailer for a different classic B+W film included. And this trailer is 16:9. That is, this 1.33:1 trailer is encoded as 16:9 with big sets of black bars to the left and right. Someone screwed up. 1.66:1 movies also benefit (although not as much as 1.78:1 and wider films) from 16:9 encoding.

[therock001]

Sorry i meant 624x352,and that is as far as 16:9 goes.

So your saying i shouldn't bother with fixed ratio,if i just set it to auto it will find the correct ar by itself?

[jagabo]

DVD only supports two aspect ratios, 4:3 and 16:9. Anything other than that will either have black bars added or the edges of the picture cropped.

On DVD the dimensions of the frame do not define the aspect ratio. A 720x480 frame is itself neither 4:3 or 16:9 but there is a flag within the video that tells the DVD player which of those aspect ratios at which to display the video.

If you resize a 16:9 DVD manually you can first resize the frame to 640x360 (or any other 16:9 ratio like 512x288) then crop away the black bars. That will always have the correct aspect ratio.

For a 4:3 DVD resize to 640x480 (or any other 4:3 ratio) and crop away the black bars. Once again, this will always have the correct aspect ratio.

Lastly, Xvid does support a display aspect ratio. That means you can encode with whatever frame size you want and have it playback with a different aspect ratio. For example, you could encode with a 480x480 frame and set the display aspect ratio to 16:9. I don't recommend this because not all players will respect the DAR flag.

[therock001]

I'm confused.I understood from what you said that the dvd contains frames including the bars,but how will i find the OAR flag?

A)For Example,i'm about to encode 4 dvds into xvid.

1 is 2.40:1, the other 2 are 2.35:1 and the last 1 is 1.85:1

I saw the the Aspect Ratios from the back of the dvd cover,but how will i know them via software say i couldn't find my covers?

B)And then will i need to set the resolution or is it best if i let AutoGK handle it automatically?

[guns1inger]

Let AutoGK work it out for you.

There are two aspect ratios on the DVD. One is for the display itself - 4:3 or 16:9. The other aspect ratio - 1.85, 2.35 etc are the original film aspect ratios. The DVD itself knows nothing about them.

If you want to calculate the aspect ratio, open the file in virtualdub, add a null transform filter, then hit the crop button. Crop the top and bottom until there are no black bars left. Now divide the width by the new (cropped) height.

[jagabo]

A)For Example,i'm about to encode 4 dvds into xvid.

1 is 2.40:1, the other 2 are 2.35:1 and the last 1 is 1.85:1

I saw the the Aspect Ratios from the back of the dvd cover,but how will i know them via software say i couldn't find my covers?

You can't. Well, you could go to imdb.com and look it up there. But there's no guarantee that the DVDs were encoded with the film's OAR. You can calculate the AR manually:

For a 4:3 NTSC DVD: take the original 720x480 frame from the DVD, crop away the top and bottom black bars, divide 640 by the height that's left. That will tell you the aspect ratio is x:1. For example, if what's left is 360 lines tall, 640/360 = 1.77. If what's left is 272 lines, 640/272 = 2.35

For a 16:9 NTSC DVD do the same except divide 853 by the remaining height. 853/480 = 1.77.

For a 4:3 PAL DVD 768 divided by the cropped height gives the AR.

For a 16:9 PAL DVD 1024 divided by the cropped height gives the AR.

[therock001]

Nice thanx a lot,i really appreciate it!

Quick question,in order to test some encodings on AutoGK,how can i create an avs script that specifies which part of a video file to be encoded?Lets say the first minute?

[jagabo]

Quick question,in order to test some encodings on AutoGK,how can i create an avs script that specifies which part of a video file to be encoded?Lets say the first minute?

Use the Trim() filter.

[therock001]

If you want to calculate the aspect ratio, open the file in virtualdub, add a null transform filter, then hit the crop button. Crop the top and bottom until there are no black bars left. Now divide the width by the new (cropped) height.

That is not entirely correct.The DVD is an anamorphic widescreen which means 1024x576 but vdub shows 720x576,which means if i crop 720x430 ->720/430=1.67,but 1024/430=2.38 which is the OAR!

[therock001]

Ii'm now trying the auto ar option of AutoGK but it detected source as 720x320 (2.25) instead of the 2.40:1 OAR.What's up with that?

Guys thanx a lot for your helpand excuse me for busting your balls with this matter but i really need to get some closure as far as Resolution and OAR go!

[therock001]

Ok the encoding finished and AutoGK chose 720x304 which according to y calculator has 1.32% error.Wouldn't it be beter if i manually select fixed ratio every time to have the least of ratio error.This occasion it would be best for 688x288 or 656x272 with ~0.5 error.

What do you guys think?

[jagabo]

Xvid uses 16x16 blocks of pixels internally during encoding. This means that frame sizes that are multiples of 16 are a little more efficient than other sizes. So AutoGK normally uses multiples of 16. I don't use AutoGK -- I don't know if it resizes to a multiple of 16, or if it resizes to the exact size required by the AR and pads with black borders. In any case you'll never notice a 1.32 percent AR error. You're TV is probably further off than that.

[therock001]

The calculator i use takes notice of 16 multipliers.Well if you say so then i trust you.Waht errors should i be concerned with?

[manono]

As I said in my first reply to you:

AutoGK is going to crop and resize to the correct AR anyway, even without your help.

If it chose 720 width, it's because of other settings you had (1-pass, target quality, maybe, or 2 CD and it compresses very well, maybe). You can, of course, choose the width you like. At whatever width, it's not going to give a high Aspect Error. If necessary, it will cut a few pixels into the video to keep the Aspect Ratio with low Aspect Error.

Waht errors should i be concerned with?

If using AutoGK, none. If you're so concerned about doing it your way, either use the more configurable Gordian Knot, or create your own AviSynth scripts and encode yourself manually. Based on your first post, that would be a recipe for disaster, although you seem to have learned a few things since then.