Cropping and resize without altering AR

Hi,

I have recorded some video clips with my stabdalone dvd-recorder.
Now I want to convert these videos to Divx to play them on a portable video player.

The original frame size is 720*576. But there are some blackborders all arond the video (maybe the overscan protection).

The original pictire is like this:


Now I'd like to cup off all these black borders (the players don't crop any pixels on the external borders of the screen) while keeping the aspect ratio.

After Cropping the size is: 700*570. I cut 16 pixels on the left, 4 pixels on right and 6 pixels on the bottom.

The final size is 384*288. So From the 700*570, can I simply resize to 384*288 without altering the Aspect Ratio (4:3).

On some other TV channels, I need to cup more data on the left.

So is there any program or formula to get the right resize ?

Thanks.

Hi-

So is there any program or formula to get the right resize ?

Yes, AviSynth, for one:

Crop(16,0,-4,-6)
LanczosResize(384,288)

Or VDub.

That doesn't alter the aspect ratio since there are less pixels than the original source ?

Or does it exist some all-in-one converters that do these steps automatically with only 1 pass encoding (I don't want autogk & gordian knot because there always do a 2 pass + compresibility test that takes ages for only videos of 3-4 minutes)

Hi-

The AR has nothing to do with the number of pixels, When making an AVI the picture is generally resized anyway. As you'll notice, 720/576=1.25:1, and not the 1.33:1 of the resized video. So, you can make your AVI for 384x288, 512x384, 576x432, 640x480, or, as the DVD would be resized, 768x576. And any number of other resolutions, and they'll all have correct aspect ratio, and they'll all have a different number of pixels than the DVD.

One last question,
My source is 720*576 interlaced, to reduce the heigh, is it better to discard one field or do a deinterlace then resize ?

720*576->discard->720*288->resize->384*288 ?
720*576->deinterlace->720*576->resize->384*288 ?

Which one is the best ?

Thanks

Hi-

If the destination height is half or less of the source height, it's safe to deinterlace by throwing away one of the fields. If the final height is more than half the original height, it's better to use a good deinterlacer. So, in the case of your original example:

Crop(16,0,-4,-6)
SeparateFields()
SelectEven()
LanczosResize(384,288)

By the way, maybe I should have known your source was interlaced, but I didn't, or didn't think of it before, but you have to be very careful when cropping or otherwise filtering interlaced video. If you capped in RGB, you're OK with that 6 pixel bottom crop (I think). The AviSynth site is down, but when it's back up, you should check out the Crop page for the cropping requirements for interlaced video. But like I said, I think you're OK with this example. But I could be wrong.

Hi Fulci-

Oh, so you go with putting back some black, to achieve low or 0 Aspect Error? Me, I hate the black so much that I'll cut a few more pixels into the video to keep the AR. When I gave him the script, I was aware that it gave about a 1% AR Error, but decided not to mention it because, 1) his res is so low that it won't be noticeable, 2) the percentage error is so low that it won't be noticeable, and 3) it opens a whole can of worms that I didn't feel like getting into. For example, do you use ITU resizing or not? Evidently you do, as do I.

Anyway, to save having to ask at VideoHelp.com every time you have to crop and resize an AVI or Vob, and to avoid having to learn the math, I'd recommend using the Resolution Tab of GKnot to get the crop and resize. Whether you use AviSynth for the job, or VDub, it'll give you the proper figures, and show you the video, so you can see what you're doing as you crop away the black. In the Options Tab you can set whether or not to resize following the ITU-R BT.601 Standard. If an AVI, you can open it directly. If an MPEG of some sort, you'll have to make a D2V in DGIndex, as it opens D2Vs, and not the MPEG itself.

You can also use AutoGK to have the whole thing done automatically; crop, resize, and the encoding. You can even set it for 384 width. It'll encode for either DivX or XviD.

Plus, if filesize isn't an issue, he can go with the 1-pass Target Quality setting of AutoGK and cut the time involved considerably (not quite in half). At that resolution, the encoding will go pretty quickly anyway.