Comments

John_Cline wrote on 10/15/2002, 5:59 AM
Actually, it doesn't distort the aspect, it corrects it. Both televisions and computer monitor screens have a 4:3 aspect ratio, or to put it another way, 1.333:1. Computer monitors are based on square pixels, for example, if your computer monitor is set for 1024x768, divide 1024 by 768 and you end up with 1.333. Now take 720 and divide it by 480, that's 1.5:1. But wait a minute, if televisions have a 4:3 aspect ratio just like computer monitors, shouldn't DV video have a ratio of 1.333:1 instead of 1.5:1? No.

DV is based on rectangular pixels, the pixels are narrower than they are tall, so it takes more of them to fill the same horizontal space than do square pixels. So if you play a DV file on your television, even though it has a ratio of 1.5:1, it displays at 1.333:1 on your TV. Circles are perfectly circular and everything looks fine. Now, if you were to watch the DV file in Media Player on a computer monitor, everything would be stretched horizontally. A circle that was photographed with your camcorder would appear on the computer monitor as a squashed oval, it will be slightly wider than it should be or, describing it another way, not as tall as it should be.

Therefore, when you are making a Windows Media file from a DV file and it will be viewed exclusively on a computer monitor, you actually want it to be 640x480, or some other size that is 1.333:1, like 320x240. This is also true of any other type of media file you will create from a DV file to view on a computer monitor.

This brings up another point that just drives me crazy.

(rant mode on)

People will create a graphic in Photoshop at 720x480 and then bring it into their project in Vegas and render it out to a DV file. Even though the canvas size was 720x480, which is 1.5:1, they created the graphic viewing it on a computer monitor using square pixels. Now that graphic is squished horizontally when viewed on a television, circles will now appear to be ovals that are taller than they are wide. Text will be narrower than they intended. Try the experiment yourself. This problem also occurs using scanned photographs or anything else generated with a computer unless the program specifically compensates for rectangular pixels vs. square pixels. When creating graphics, you need to start with a 720x540 canvas, create the graphic and then as the very last step, resize it to 720x480 and then pull it into Vegas. It won't look correct in your graphics program, but it will display correctly on the TV. If your using scanned photographs, crop them at 1:333.1 and then resize them to 720x480 as the very last step. (actually, I use 1440x1080, which is exactly twice as wide and tall as 720x540.)

Folks in PAL-land have the same issue, but the math is somewhat different. Their TV's are still 4:3 (1.333:1) but their DV video files are 720x576, which is 1.25:1. They have the opposite problem than the NTSC folks encounter, their DV pixels are rectangular, but theirs are slightly wider than they are tall. They need to create graphics at 768x576 (1.333:1) and then resize to 720x576 (1.25:1)

Anyway, you want your Windows Media files to be 640x480 so they display with the correct aspect ratio when viewed on a computer monitor.

(rant mode off)

John
watson wrote on 10/15/2002, 7:41 AM
Thanks for the explanation. I understand that it should be correct but my eyes are telling me the rendered video is off. I wonder what is going on here. Perhaps it is not adjusting the ratio like it should.
I'm using the windows 9 codec.
I will do some experimenting. Thanks for your help.

W
prairiedogpics wrote on 10/15/2002, 7:55 AM
I do this all the time: source footage is 720x480 DV AVI, and I render it as a WMV file. But when I render it, I choose the WMV template, click on Custom , and on the next screen there's a drop down menu that says something like "custom size" (I'm not in front of my VV3 setup right now), and from that drop down menu you can choose "Keep Original Size" or something like that. The resulting file is 720x480 with no distortion. I hope this is what you're asking. Sorry to interject if it's not.

Dan
John_Cline wrote on 10/15/2002, 8:55 AM
But viewing 720x480 DV video on a computer monitor WILL be distorted unless the program specifically compensates for it. (The video preview window in Vegas will compensate if you have selected "display square pixels" in "Preferences" under the "video" tab.)

Shoot a perfectly circular item straight on with a DV camera, capture it and view it with Windows Media player, the circle will be an oval. Absolutely and positively guaranteed.

It is SO frustrating to me that so few people actually understand the difference between square and rectangular pixels and when and how to compensate for the difference. I've been trying for years to figure out an effective way to explain it and I guess I haven't yet figured out a way.

John
prairiedogpics wrote on 10/15/2002, 9:08 AM
Yes, I understand that. Raw 720 x 480 DV AVI footage viewed on a computer will appear distorted (e.g., through Windows Media Player). I was saying that if you RENDER this footage in VV3 using a WMV template (and going to custom and choosing "keep original size"), you will create a WMV file that appears with NO distortion (not stretched horizontally) when viewing thru Media Player. After all, this format is meant for computers, is it not?.

Please tell me if I'm wrong; I DO want to understand this stuff. And John, as a long-time reader of this forum, I do appreciate your detailed and meticulous explanations. Keep them coming.

Dan
SonyDennis wrote on 10/15/2002, 12:19 PM
Dan:

You should be able to bring in rectangular pixel DV (720x480 PAR 0.909) and render to WMV (let's say 640x480) and have no black borders. I do this all the time. If you shot a circle with your camcorder it will be a circle in WMV. When you're displaying the DV in Vegas, it might be a circle or oval, depending on the setting in the Video window (right click, "Display [using] Square Pixels" -- if ON it should be a circle, OFF will be an oval (distorted).

///d@
tadpole wrote on 10/15/2002, 1:56 PM
I hope the immortal John_Cline hasn't been flustered off this thread & is still here with us! We're a bit stubborn, but your wise teachings will eventually prevail!

Re-world example:
I want to add some generated video to a vv project that is comprised of 720x480 NTSC DV footage - Project is destined to be viewed on 4:3 TV - via rendering project to MPEG 2 (video settings w-720 h-480 aspect ration 4:3), then to DVD

The generated video i will be importing is a Flash animation exported as an .avi
SO - in order to prevent distortion on my final TV 4:3 viewing format:

1.)I should create my flash file on a 720x540 canvas & render to .avi with those dimensions
2.)Now, i need to resize it - so i bring into something like VirtualDub, add a resize filter, resize to W-720 h-480? (any recommendations on Filter mode? nearest neighbor, bicubic etc?)

Then import to VV, render, & everything is a-ok?
(yes, i probably could've experimented before i came in here asking all these questions, but thats the joy of great forum communities ;)

thanks
(if i'm still WAY off here - totally my fault jcline! your explanations r great, i'm just stupid)



John_Cline wrote on 10/15/2002, 3:12 PM
Daniel:

If you create a WMV file from a 720x480 DV file, as long as it ends up at 640x480, or 320x240 or some other size with a 1.333:1 aspect ratio, then it will have the correct aspect ratio when viewed on a computer. A 720x480 DV file when viewed on a TV will have the same aspect ratio as a file viewed at 640x480 on a computer monitor. The television does the 1.5:1 to 1.333:1 conversion automatically.

tadpole:

Yikes! Now I'm immortal. My critics are going to just love that! :)

Yes, create your Flash animations at 720x540 and resize them to 720x480 in Virtual Dub. Flash animation aren't interlaced, otherwise this would be more complicated, and since they aren't, create the animation and render uncompressed at 720x540 and get into Virtual Dub, use either the Precise Bilinear or Precise Bicubic resize filter and resize it to 720x480 and save it as an uncompressed AVI. (Just keep it uncompressed all the way through. No sense in compressing to DV until the final render in Vegas using the terrific looking Vegas DV codec.)

Speaking of interlacing, to create an animation with "creamy smooth" motion, it would be best to create your animation at 60 frames per second or create it at 30 frames per second and make it twice as long as you want it to be. You could then double the speed of the file and interlace consecutive frames so that each frame of your animation ends up as a separate field in the video. It would take two frames of your animation to make one frame of video. You would end up with 60 fields per second interlaced instead of 30 frames per second progressive. This would give you twice the "temporal" (time) resolution. Unfortunately, I don't know of a way to do this in Vegas or Virtual Dub. I use Adobe Premiere to pull off this trick. It sure does make a difference though.

Anyway, back to aspect ratio; You can always test the final aspect ratio by creating a perfect circle in a 720x540 project in whatever you're using to generate your Flash animations and go through all the conversion steps and view it on the TV. If the circle is still circular, then the processing steps you have chosen are correct.

John
tadpole wrote on 10/16/2002, 2:32 AM

alright! you even answered my follow up question about frame rates b4 i even asked it.

Ladies n gentlmen,,, again....mr john_cline
::cheers::

thanks for the tips!
SonyDennis wrote on 10/18/2002, 11:09 PM
John, great tip on rendering animations at 60fps. If you only render to 30p it looks out of place in 60i video. By rendering to 60p, Vegas takes half the scanlines from each frame and makes 60i from it, and, as you say, the motion is silky smooth.

Thanks.
///d@