help understanding crop/add border

[newbie04]

Could someone explain the difference between these:

crop(8,4,-8,-12)
AddBorders(8,4,8,12 )

crop(8,4,-8,-12)
AddBorders(8,8,8,8 )

crop(8,4,-8,-12)
addborders(0,8,0,8 )

I guess I can't visualize what is going on... how are things getting shifted?
My source is 720 x 480.

[newbie04]

ok i had some time to try things out...

1st one doesn't change anything

2nd one appears to give me equal borders all around

3rd one not sure
--------------------
Have another question though:

From what I read if you have lots of noise on the edges you would waste bitrate, and it is better to add a solid color border.

So I have my DV avi file of a show on tv, which is 720 x 480. I don't have a DVD burner, so decided to make a CVD (352 x 480) on CD-R until I can transfer later to DVD.

Okay, so the DV file has tracking noise on the bottom and some borders on all the other sides, so when I wrote my AVISynth script, it looks something like this:

LoadPlugin("Convolution3d.dll")
avisource("D:\test.avi")
crop(8,2,-8,-14)
.
.
.
AddBorders(8,8,8,8 )
LanczosResize(352,480)

So with the above, I have black borders all around and this is fine for watching on a tv, since I will never see them.

But what about if I make clips for viewing on the web?
How do you maintain I guess the correct size/aspect ratio if you don't add in the borders?

[bunyip]

In your example 1, it appears that nothing changes because you are replacing exactly what you cut with black, but it in fact covers up any edge noise you may have and given it a crisp even edge. The visual aspect ratio when played back remains the same, and the video position is unchanged.

In example 2, you cut the edges down to the actual video (removing black edges) and replace them with an even 8 pixel border all round, but what you have also done is shifted the video 4 pixels down the screen. The visual aspect ratio when played back remains the same.

In example 3, you have shifted the video down 4 pixels, removed existing black borders from the left and right and stretched the width by 16 pixels (after a resize). The visual aspect ratio is slightly altered because the picture width has been stretch slightly.

For use on the web or just for play-back on a PC you generally only need to crop the borders and resize. The video will be stretched in both directions to compensate but usually it is not visually detectable, because the stretching is in both directions so the resulting visual ratio is still close to the orginal.

[newbie04]

Thanks a lot for the explainations. It really helps!

If I do for:

CVD: Crop > AddBorder > Resize 352x480 and

DivX: Crop > Resize 352 x 240

everything will just work out fine?? 8)

[bunyip]

Yes - both should play back at 4:3 resolution and look OK - providing that you're not cropping large amounts so that the final video becomes visually distorted.
Remember also that CVD is not a universal standard so systems that don't support it may play back distorted, or not playback at all.

If in doubt - experiment.