changing avi resolution

[doubleJ]

I don't know of a better place to ask this, so...
Is there a quick/dirty program to resize an avi? I have some tv rips that I want to make smaller but I encoded them, previously, at 720x480. I was hoping for somewhere in the 5xx range so I could fit 4 on a cd instead of 2.
Thanks...
JJ

[Manao]

If you want to change the resolution, you'll have to reencode completly your tvrips. The simplest way is to use VirtualDub, load your avi inside, use a filter to resize it to a lower resolution, and then encode it ( with XviD / divX ). But, of course, you'll have a loss in quality, due to the lowering of the resolution, and to the reencoding ( which is a lossy process )

If you have any questions on the process I described, please read Doom9's guide on virtual dub and on DivX5 before, they should answer all your interrogations.

[doubleJ]

Ah...
Thanks for the info...
If I'm going to loose quality, then I don't care to do it. Part of the reason why I wanted to resize was that the pq wasn't that great, anyway (for some reason, my xmpeg encodes looked like crap for a couple months). I figured that low quality and high size didn't work.
I guess I'm suprised that an ndub type of program hasn't been made that can do that without re-encoding.
JJ

[Manao]

It is simply not possible. When you encode in MPEG-4, you are converting a serie of pictures into a serie of motion vectors ( calculated for every 8x8 squares of each pictures ), and a serie of fourier's coefficients for each of these squares, calculated by substracting to the square the motion estimated square from the previous compressed frame.

So if you want to do it without reencode, you have to drop information. If you drop motion vectors, trying to average them for 16x16 blocks, you'll see a degradation in the picture, getting worser when you're farther from a keyframe, because the fourier's coefficients won't be right anymore. If you drop fourier's coefficients, you're making the motion estimation during the encoding less precise, and you'll get the same bad results.

And when I say bad, it's _really_ bad, not just blocky or something. You wouldn't recognize some part of the video.

[bond]

theoretically it is possible to change the resolution of a mpeg-4 stream (doesnt matter which container is used: avi, mp4, mkv, ogm...)

the only problem is that no tool till now can do it