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Topic: Trancode AVI to different aspect ratio? (Read 7766 times) previous topic - next topic
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Trancode AVI to different aspect ratio?

I've only recently gotten my hands on a DVD+-R/RW drive and have just started playing with video files.  After an hour or so searching forums and the net, I just can't find an answer for my problem.

A while ago I got a bunch of .avi files of TV programs that are wide screen with an aspect ratio of 20:11 when played back on computer video software. 

Is it possible to transcode those .avi files to the aspect ratio of a standard TV, which I think is 4:3, right, so I burn them to a DVD that will play through the home DVD player and fill the TV screen?

Thanks,

TS

And oh... thanks for all the great advice on other threads on this BenQ DW1640. I picked up an OEM model online  for $39 >with< shipping... and seems to be working really well so far.
Geopoliticus Child Watching the Birth of the New Man

Trancode AVI to different aspect ratio?

Reply #2 –
Reversing your order:

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http://www.doom9.org/mpg/dvd2svcd-avi.htm
[{POST_SNAPBACK}][/a]

Since I've going to DVD, I guess I'll not need that tutorial -^

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[a href="http://www.doom9.org/mpg/avi2dvdr.htm]http://www.doom9.org/mpg/avi2dvdr.htm[/url]
[{POST_SNAPBACK}][/a]


So it looks like the pertinment line there is:

"Replace the 2nd number with the appropriate number taken from the calculations above."

The value from GSpot in that example was 640x272, 1:2.35 - And they want to maintain the original aspect ratio.  So they would change the value in the example script from:

BicubicResize(720,272)

To:

BicubicResize(640,272)

Right?

The aspect of the video files I'm dealing with is: 640x352, 20:11 - or 1:1.82

If I want to convert it to the standard NTSC TV format of 4:3 - or 1:1.33, I think this would be the math:

*  x/640 = 3/4
*  x = 3x640/4
*  x = 480

Gosh... where've I seen that before ...    So I'd want the 3rd line in that script to read:

BicubicResize(640,480)

Is that right?

EDIT: I just looked at [a href="http://www.doom9.org/mpg/avistretching.htm]this[/url] where is says "encoder expects a 720x480" and am wondering if that line should read: BicubicResize(720,480)

Then I guess I'd just eliminate the line: AddBorders(0,104,0,104)

And as these TV files don't have subtitles, I guess I won't need the 1st 2 lines either:

LoadPlugin("c:\windows\system32\vobsub.dll")
avisource("moviename.avi")

Am I making sense here, or have I missed something obvious to the trained video mind?

Thanks,

TS
Geopoliticus Child Watching the Birth of the New Man

Trancode AVI to different aspect ratio?

Reply #3 –
Bleh, that guide is laughable and you are not making sense at all.

Your TV is 4:3, DVDs have a resolution of 720x576 for PAL or 720x480 for NTSC (oh, and people please forget about ITU for a moment...) Your video has a PAR of 1:1 (i hope) and a DAR of 20:11.

Now the question is: do you want to make an anamorphic (16:9) DVD or a 4:3 DVD?
- For an anamorphic DVD I would just resize to 720x480 or 720x576 since it probably was full screen anyway but an AR error was introduced to keep things mod16)
- For a 4:3 DVD, you will need to resize to 720x432 for PAL and pad the rest with black border to get 720x576, or 720x352 for NTSC and pad the rest with black to get 720x480.

Numbers are a bit screwy here since im a bit unsure about the source, but its probably a lot closer than what you were doing.
"We cannot win against obsession. They care, we don't. They win."

Trancode AVI to different aspect ratio?

Reply #4 –
Okay... bear with me here... this is all new to me in the past day or two.

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Your TV is 4:3, DVDs have a resolution of <snip> 720x480 for NTSC (oh, and people please forget about ITU for a moment...) Your video has a PAR of 1:1 (i hope) and a DAR of 20:11.

Those are the values of the .avi files I want to change the aspect for.  They now play back in wide screen with black above and below the picture.  Can that be changed?

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Now the question is: do you want to make an anamorphic (16:9) DVD or a 4:3 DVD?

From what I've read, 'anamorphic (16:9) DVD' is by definition wide screen, right?

As I pointed out in my 1st post, the original files are wide screen.  The whole purpose here is to, as I wrote "transcode those .avi files to the aspect ratio of a standard TV".  So I'm assuming that means going to the 4:3 DVD format... right?

I'm a bit confused about the aspect ratio value, and corresponding pixel ratio.  They are directly related... right?  The pixel value 'NumberXNumber' will always correspond directly to the '1:X' ratio... right?

It seems I need to learn just where to start determining which 1st pixel value to start at.  In my last post, I apparently made the mistake of entering BOTH values, 640x272 into the script.  I didn't catch the instruction to only replace the 2nd value.

Why a 720x480 ratio is used for DVD playback instead of 640x480 I'll have to find out.  But it appears the DVD playback device will recalculate it's output to fit the standard 640x480 TV screen.

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- For a 4:3 DVD, you will need to resize to <snip> 720x352 for NTSC and pad the rest with black to get 720x480.

Okay... now I'm really confuddled...    If my files presently have an aspect ration of 640x352, 1:1.82, what values would I need to enter in this script command to get the file to fill the screen on a standard NTSC TV?: BicubicResize(x,x,x,x)

And if I need to pad (why??), will I then need put values in the 'AddBorders(x,x,x,x)' script command?

TS
Geopoliticus Child Watching the Birth of the New Man

Trancode AVI to different aspect ratio?

Reply #5 –
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Okay... bear with me here... this is all new to me in the past day or two.

Okidoki.

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Those are the values of the .avi files I want to change the aspect for.  They now play back in wide screen with black above and below the picture.  Can that be changed?

Yes and no. Yes, if you don't mind people will look like the coneheads, or that about 27% of the picture area is cropped off. No, if you do mind these things.

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From what I've read, 'anamorphic (16:9) DVD' is by definition wide screen, right?

Yep.

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As I pointed out in my 1st post, the original files are wide screen.  The whole purpose here is to, as I wrote "transcode those .avi files to the aspect ratio of a standard TV".  So I'm assuming that means going to the 4:3 DVD format... right?

Not necessarily. You will just get black bars on your TV if you play 16:9 DVD.

Quote
I'm a bit confused about the aspect ratio value, and corresponding pixel ratio.  They are directly related... right?  The pixel value 'NumberXNumber' will always correspond directly to the '1:X' ratio... right?

No it won't. (and this is what causes your confusion)

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Why a 720x480 ratio is used for DVD playback instead of 640x480 I'll have to find out.  But it appears the DVD playback device will recalculate it's output to fit the standard 640x480 TV screen.

A TV screen IS approximately 720x480. But unlike for PC screens where a sample value (a pixel) represents a square, a sample value for a TV represents a rectangle.

A graphical explanation can be found here --> click

I hope that will take away some of the original confusion and not add too much new.

Oh and please stop reading that guide, it is already making you write things like
Quote
NTSC TV format of 4:3 - or 1:1.33

which is both from a mathematical and practical point of view completely wrong.

The correct way would be saying 1.33:1, 2.35:1, etc.
"We cannot win against obsession. They care, we don't. They win."

Trancode AVI to different aspect ratio?

Reply #6 –
Stephen,

Thanks for taking the time to sort through these things with me.  I did in fact get my major questions worked out last night after finding a piece of software from River Past called Video Perspective 5.0.4

Running that, I finally saw the folly of what I was trying to do.  It was able to stretch the video to fill an apsect ration to match a standard NTSC TV.  But as you pointed out, one method stretched and distorted people to the 'conehead; perspective you referred to.  The other method (pan and scan) cut off the sides of the image in a similar manner as the method used to reformat commercial movies to the standard NTSC TV perspective.

However even after reading through the info you pointed me to, as well as the info on the page that one pointed to here, I'm now wondering how a digitally produced wide screen TV program gets displayed on an old standard TV.  It would seem some kind of panning would have to be used... but the old TVs wouldn't have such technolgy.

Quote
Quote
So I'm assuming that means going to the 4:3 DVD format... right?
Not necessarily. You will just get black bars on your TV if you play 16:9 DVD.

Well... my objective was to get the image to fill the standard NTSC TV screen with the picture sans black bars.  That would necessitate a 4:3 perspective, wouldn't it?

Quote
Quote
I'm a bit confused about the aspect ratio value, and corresponding pixel ratio.  They are directly related... right?  The pixel value 'NumberXNumber' will always correspond directly to the '1:X' ratio... right?
No it won't. (and this is what causes your confusion)

That URL you pointed me to finally explained FAR, PAR and (well at least intruduced:) DAR, and light is slowly beginning to dawn on me here.

Quote
A TV screen IS approximately 720x480.

Ahhh... okay... thanks for that.

Quote
Quote
NTSC TV format of 4:3 - or 1:1.33
which is both from a mathematical and practical point of view completely wrong.
Hmmm... why is that?  Is that ratio always supposed to represent the X and Y axis in the same order?  In other words, is the 1st value always support to be either X or Y, and the 2nd value the other?

In that case, I assume that when referring to video aspects, the ratio is always supposed to be represented in this manner:

X(Horizontal):Y(Vertical)

Yes?

Thx,

TS
Geopoliticus Child Watching the Birth of the New Man

Trancode AVI to different aspect ratio?

Reply #7 –
Quote
I'm now wondering how a digitally produced wide screen TV program gets displayed on an old standard TV.  It would seem some kind of panning would have to be used... but the old TVs wouldn't have such technolgy.

I don't know the answer to that one.

Quote
my objective was to get the image to fill the standard NTSC TV screen with the picture sans black bars.  That would necessitate a 4:3 perspective, wouldn't it?

Yes. But you have seen what trying to do that results in now.

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I assume that when referring to video aspects, the ratio is always supposed to be represented in this manner:

X(Horizontal):Y(Vertical)

Yes?

Yep. This also counts for resolutions, they are always widthxheight. I know this is merely a matter of convention, but for PAR the difference between 10:11 and 11:10 is quite big, so just do it like everybody else is doing it.
"We cannot win against obsession. They care, we don't. They win."

Trancode AVI to different aspect ratio?

Reply #8 –
Thanks again for helping to straighten me out here Stephan, and for pointing me to the www.seemoredigital.net site.  It looks like a good site to get a handle on some on the basic principles of video formatting.

Now to see if I can capture video from some of my old VHS cassettes to digital files and burn them to DVDs for watching on the TV... along with a few other projects that have been waiting for a DVD recording drive and video capture card.

TS
Geopoliticus Child Watching the Birth of the New Man