Aspect ratio not clear at all for DV-Divx

[bluesix]

Let's assume for 1 second that I don't have the time to study sampler rate, pixel frequencies, sampling matrices.

I simply want to go from A to B

A) source: 720x480 uncompressed DV avi.

B) result w x h (proper aspect ratio) Divx avi

I occasionally will need to crop at least 6 pixels from the bottom due to noise from older tapes. I am currently using Premiere because I understand Virtual Dub with all its whistles still requires some complicated process to handle DV.

Premiere gives me 4 diffent options:

Video filters: Crop. Resize

Movie settings: Frame Size: defaults to 720 x 480

maintain 4:3 ratio box (check/uncheck)

Special processing: Cropping settings with a <scale to> box

:confused:

What and where do I make these aspect changes to? If I leave everything unchanged, the 720x480 divx clip looks a little fat. At 640x480 it appears thin.

Please help.

If I understand correctly, the suggestion is to crop 8 pixels off the left and right side. When do I do that? And what about the extra cropping at the bottom? is the ratio i am going for 704x480? I could then crop six pixels off the bottom and wind up with 696x474.

Also I can't seem to figure out how to accomplish 2 pass divx4 encoding in premiere. that i can live with.

-bluesix.

[theReal]

I always use Gordian Knot to calculate the right aspect ratio.
In the resolution tab, check NTSC as the input resolution, then check NTSC non-anamorphic 4:3 for the input pixel aspect ratio. If you want to crop, check "pixel" and enter your cropping values.
Then you'll get the perfect resizing value in the bold WidthxHeight fields in the middle (best leave the values divisible by 32 and 16 - even when the aspect error is 2% you won't notice that little error)

[bluesix]

Thanks. That Gordian knot calculator was very helpful. Now that I have my target size of 640x464 I set my frame size in Premiere to 654x476 and then under the special processing settings I crop 12 pixels off the top and bottom and 16 off the sides. I get a final clip frame size of 640x464.

Is that about it? Is that the proper aspect ratio?

-bluesix.

[bluesix]

According to Gordian's Knot, the aspect ratio for an uncropped clip should be 640x464.

My eyes might not be that good but the movie looks a little fat.

What am I doing wrong.

Input source: 720x480 dv type 2 avi.

-bluesix.

[bb]

According to the F.A.Q. 640x464 is ok for PAL (verified on my personal camcorder). I'll have to investigate the proper resizing values for NTSC, they might be different, but because of the rounding due to the mod 16 height constraint it may turn out that the same resolution is recommended for NTSC. Don't know yet, but I'll extend the F.A.Q. as soon as I know.

Be aware of the fact that not all monitor resolutions have a 1:1 aspect ratio. E.g. 1280x1024 monitor resolution is 5:4, not 4:3, thus the pixel aspect ratio is different (because the monitor size stays the same, of course). If you use this monitor resolution, switch to 1024x768 and see if the problem's gone.

I highly recommend to assume 1:1 pixel aspect ratio in order to calculate the resizing. If you need to display the video on device having a different pixel aspect ratio (e.g. a TV set, or a computer monitor with a strange resolution), then let the player do the final resizing.

bb

[Wilbert]

According to the F.A.Q. 640x464 is ok for PAL (verified on my personal camcorder). I'll have to investigate the proper resizing values for NTSC, they might be different, but because of the rounding due to the mod 16 height constraint it may turn out that the same resolution is recommended for NTSC. Don't know yet, but I'll extend the F.A.Q. as soon as I know.

The same for NTSC:

720*10/11 / 480 = 1.363636364

640/(464+16) = 1.333333333
640/464 = 1.379310345
640/(464-16) = 1.428571429

thus resizing to 640x464 is the most accurate.