Crop or Resize?

[Tolwyn]

To make 1024x768, 800x600 etc. (Computer resolutions) of captured material compatible with DVD and all the ratios and stuff...

What's a recommended procedure (notice I didn't say "best" ).

Resize or Crop?

border?

A little lost.
Also, where can I find the handy-dandy aspect ratio and resolution table for the different formats?

I'm ratio and resolution stupid.

[Gees]

Ready for some reading? :c)

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

There you go. :c)

[Tolwyn]

Thank you!
Why couldn't I find this guide?

[Gees]

You're welcome. It might be hard to find that one because it's under "General Video Questions" or something like that. :c)

I was lucky to have seen it when it was written and remembered who authored it, so I looked it up that way. :c)

[Gazorgan]

I do a combination or crop, mask, and re-size. I do this to maintain my aspect ratio, while ending up with a valid/suitable size.

The order can be important.

How are you getting 1024x768 captures? And of what? Unless you have an HDTV mini-cam, there aren't a lot of hi-res sources. Broadcast NTSC isn't really any higher than 352x480 (and interlaced at that).

[trevlac]

To make 1024x768, 800x600 etc. (Computer resolutions) of captured material compatible with DVD and all the ratios and stuff...

I'm ratio and resolution stupid.

It all depends upon your source. If you "captured" your screen, then for NTSC you should do the following:

1. Resize to 712x486
2. Crop the 486 to 480
3. Crop or pad the 712 to 704 or 720

No Kidding !

Go here for the gorrrry details: http://www.uwasa.fi/~f76998/video/conversion/

The guide pointed to was really for "normal" video source, such as DVD, DV, or some capture cards. If you have one of those, use it. If you have PAL, I believe you resize to 702x576 and pad to 704 or 720.

Edit: 711 is more precise than the 712 numbers above. Some times computers like numbers divisible by 8 much better than a number like 711.

[Tolwyn]

You know, I didn't think I'd get confused, but that guide just made it worse.

If I have a 800x600 source or 1024x768 source (capturing using Fraps from a video game), the "aspect ratio" is a byproduct of the resolution, not the other way around...

I can capture in 800x600 all the time, then, as I'm likely to get a better framerate before interpolation to 29.9xxx whatever.

I'm still confused, though.
I'm not worried about widescreen, as everything that I capture, unless I'm goofing around for "special affect" is going to be 4:3...

I think I'm using Virtual Dub for the editing portion... I'm not sure yet. I haven't made it that far.

Does the encoder handle the risize (ala DIVX), or do I do that FIRST and THEN encode with no resizing or cropping?

What program "pads" and what's the difference between padding and cropping? Does padding = "add border" ?

So before I encode to MPEG2 (DVD), I want my stuff to be 4:3, which would be 720x480? Do I add the border(s) before encoding?

Or would the encoding autmatically make/stretch my stuff appropriately?

It's like the guide skirts what to do, and it just talks about "what is."

I dunno. Maybe I'm just tired.

What resolutions is DV? Does any resizing need to happen before final encoding for DVD?

Can I work, in one "clip" or "scene" with different resolutions but same ASPECT for the final product?

[trevlac]

If I have a 800x600 source or 1024x768 source (capturing using Fraps from a video game), the "aspect ratio" is a byproduct of the resolution, not the other way around...

You "captured" from your PC screen in square pixel at a 4:3 aspect ratio. Follow my steps above.

I think I'm using Virtual Dub for the editing portion... I'm not sure yet. I haven't made it that far.

Does the encoder handle the risize (ala DIVX), or do I do that FIRST and THEN encode with no resizing or cropping?

With Virtual Dub filters you can resize (smart resize) and crop (null filter)

What program "pads" and what's the difference between padding and cropping? Does padding = "add border" ?

Pad = add border

.....

It's like the guide skirts what to do, and it just talks about "what is."
The Guide tells you what to do if you are already at 4:3 in non-square pixels. You are in square pixels. You have to convert.


What resolutions is DV? Does any resizing need to happen before final encoding for DVD?
DV is 720x480 non-square pixels. Perfect for DVD.

Can I work, in one "clip" or "scene" with different resolutions but same ASPECT for the final product? I don't know, but logic says yes

If you plan to mix DV with this PC generated stuff, I think a bigger problem will be color. When you jump back and forth, you will be able to tell. Hopefully it is not distracting.

[Tolwyn]

This is just a stumbling block for me.
I have to think in pixel size, not aspect ratio.

720x480 is 4:3? This is suitable for DVD?

Is any 4:3 aspect suitable for DVD if encoded in MPEG2?

I want to avoid bicubic resize if at all possible; and would rather have the hardware (DVD Player) do that.

Why 704?

Which is "more often used?"

[trevlac]

Here is a riddle for you.

Why is 720x480 3:2 not 4:3 ?

If you know the answer to then you really know. If you don't want to figure this out, then you could just follow my steps.

Hint:

Pixels are 2 dimensional objects. Inches are not. Measuring in pixels == measuring in inches IF the pixels are sqare (h=w). TV Pixels (h<>w). PC Pixels (h=w).

I'd be happy to explain. Or you can test, read, etc....

PS: Look under what is DVDR at top left to see valid DVD size.

[Tolwyn]

Jesus. Seriously. This is where I'm just lost.

What is full screen resolution for TV?
Give me pixel resolution.
What is the aspect ratio?

What are legal wxh that burning to a DVD and watching it on my TV with no stretching?

[Gazorgan]

Computer pixels are square.

TV Pixels are rectangular.

720x480 is 4:3 on a TV (mostly)

640x480 is 4:3 on a Computer


If you work in 640x480 for your computer captures you will be fine. Going higher res isn't going to do you any good, because a TV can't display the information. 800x600 is another option, and it will resize down nicely as well. I suggest a couple of 30 second test captures to paly with.

Should we bring up interlacing now? Nah, we will save that for the final encoding to mpeg2 (that's about the last step) for DVD.

Skinny heads/Fat heads are another issue, but a little tweaking in re-sizing will make it go away.

[Tolwyn]

I have an AVI file that is 352x240.

That's 1.46 decimal aspect. Have no idea what the ratio is.

What do I need to do to this AVI file to get it to play right on TV, full screen.

Must it be resized to 720x480?

I understand "non-square." My monitor is 1280x960 resolution; 1.33 decimal. Just like NTSC 4:3. Right?

My question is, are there legal pixel requirements, or just aspect requirements for AVI transfer to DVD (MPEG2 encoding).

Must I pad/crop everything?

[Tolwyn]

Yes, this is a concept I do not understand at all.
Mathmatically, it's incorrect.

640x480 is a true 4:3 ratio (1.333333:1)
720x480 is a true 3:2 ration (1.5:1)
How can anyone say that 720x480 is a 4:3 ratio for TV?

Jeeze. I've forgotten how to figure x:y ratios. How do convert from decimal 1.333 to a ratio? Too much on my mind today.

So. I'm going to need help with this. My mind just can't handle mathematical inconsistencies.

I thought my question was simple.

What do I need to do to ANY video source to make it legal to playback on my DVD player.

Is there a TARGET resolution I have to either resize to or pad? OR can I just match the aspect ratio and it will work?

640x480, 800x600, 1024x768, 1280x960 are all the same aspect ratio.

[Tolwyn]

trevlac.
Yeah. Please explain it to me because I don't understand.

I see what you're saying, but don't understand the "why" behind it.

Why is TV's h != w ?

Now, do I need to compensate for that on the computer and "squish" all my video before outputting to DVD????

Sweet baby Jesus this should be easier than this.

[FOO]

Here it is in brief.
There is a Sample Aspect Ratio which is the actual dimensions of the
pixel array. DVD REQUIRES a limited set of those.
720 x 480
704 x 480
352 x 480 and a few more

There is a Display Aspect Ratio stored in the MPEG2 data. It instructs
the player to display the data as it says regardless of the SAR.
The player essentially resizes the horizontal on the fly .

So you can have a 720 x 480 SAR and a 352 x 480 SAR video
look identical on your TV because they may both have a 4:3 DAR set .
SVCDs are 480 x 480 SAR but look like 4:3 because their DAR is 4:3

One way to observe this is to watch the video with a program like Vdub
which ignores the DAR. You will then see 352 x 480 look squished vertically.

[Tolwyn]

Ok. Clouds are clearing a little.

Where do I set the DAR?
Is this done automatically by the encoder? TMPENC or something?

Will my SAR of 720x480 with a set DAR of 4:3 look correct on the TV as it does on my computer?

[trevlac]

What do I need to do to ANY video source to make it legal to playback on my DVD player.

Take a deep breath. I am not an expert, but I'll try to answer your question 1st.

IF your source came to your computer from a video source thru a standard piece of equipment. It is already in the right aspect ratio.

Since DVD has a limited number of valid sizes, you can follow the guide to change the sizes with this type of source, using "normal" logic to keep the aspect ratio. ie. 352x240 to 704x480 resize is ok with regard to aspect. To go to 720 add borders, etc.


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The Fun Stuff

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Confusion with Widths

• TV screen is 4:3 (measure it in inches. This = 1.3333)
• PC screen is 4:3 (measure it in inches)
• Measurement of PC screen in Pixels is 4:3 (ie 800x600)
• Measurement of TV screen in Pixels is ?????

Everything but the last item should be clear.

On the last item:
Inches are 1 dimensional. Pixels are 2 dimensional. Measurements in square pixels up and down and side to side are as inches. Measurements in non-square (rectangle) Pixels are not the same.

Why the he11 would anyone use a non-square unit of measure?

A TV active picture is 711x486 PIXELS (in terms of a digital picture seen on an analog TV, NTSC). 711/486 is NOT its aspect ratio, because the pixels are not square. The 486 is a fixed number due to the way a TV scan works. The 711 is due to a standard ITU 601. The standard says sample the 52.66666 microsecond active picture scan line at 13.5 MHz. 52.66666 * 13.5 = 711. The 13.5 in the standard screws everything up. However, there are good technical reasons for this number.

See this link for further on this : http://www.quantel.com/domisphere/infopool.nsf/HTML/565C7D89F2D64F3680256C8000444A4D

Conclusion

If you need to go from square 800x600 to non-square, get the height to 486 using a "lock aspect ratio" type of resize. Then streatch the width to 711 to make up for the tall skinny pixels on a tv. Streatch by 79/72. Finally add boarders to go to 720 on the sides and crop to 480 for DVD compliance.

How do we get 720x480 ? Well the same standard says DIGITAL stuff (IE DV or DVD) is that size. These numbers are divisible by 16. (So is 704).

When your dvd player outputs to analog, it looses the extra boarders on the sides and addes 6 black lines on the bottom. That is because it is going from the 601 standard digital stuff to the 470 standard analog stuff.

This was quick. Have to go ... but be happy to do a Q&A.

[Tolwyn]

So, by convention should I just stick with 720 instead of 704?

Here's what I need you to see to visualize how I'm applying your words.

Here's the original image, 1024x768:


Here's what I need it to "look like" before burning DVD:



(pretend that the JPG is a video window)
So, watching it "as is" on my PC, it's going to look stretched; but that's so it doesn't look "skinny" when it's on my TV?

[trevlac]

You got it !

I think the key thing to understand here is you are doing something special. You did not get your source in a "normal" way. It was computer generated Right?

As far as the DAR and SAR go, your DAR is 4:3. That was always clear because you see it that way on the computer 800x600. The only other real option for DAR is 16x9 and I'm sure you don't want that.

SAR 1:1 on the other hand is not clear to me. I think the intent of that is for playback on a computer.

Specify the aspect ratio in Aspect Ratio. The value which can be
set here is SAR 1:1, 4:3, or 16:9. SAR refers to "Sample Aspect
Ratio". If SAR 1:1 is selected, the aspect ratio of each pixel becomes
1:1. Therefore, for example, if a footage whose frame size is 720×480
is encoded with SAR 1:1, the display aspect ratio will be 3:2.
4:3 is an aspect ratio used for a general TV monitor. If the footage is
wide screen, 16:9 may be appropreate. The MPEG-2 playback device
(e.g. DVD player) refers to this setting, and corrects the aspect ratio
when outputting data to a TV monitor.

SAR and DAR seem to be mutually exclusive. You want to have a DAR of 4:3.


Another thing to note is the plane on the upper left will (most likely) not be seen on a TV due to overscan. Read the glossary for overscan if you are not clear on this. To see more action on the screen, Add 5% black borders around the picture as a 1st step.

ie. If you start with 800x600 add black to 880x660, resize to 712x486, crop/pad to 720x480.

Note: One resize would be better than the 2 I mentioned above. The 2 were just to clearify the process.


Finally ... I wanted to add that I am not in the video field. I've just been reading about this stuff and doing my own tests. You should do some small samples and see the results on your TV before you follow any advice given free on the internet. But I think I am right :P

Here is a link about Aspect Ratio. I belive DAR is the Picture Aspect Ratio mentioned. Pixel Aspect Ratio (the second def) is your problem.