Question about Compressibility/Resolution

[jang0]

Ok, my situation:

I want to encode a 21:34 min VOB-File (Pal DVD Source 4:3 AR) with dvd2avi -> avisynth -> virtualdub to Xvid, while my desired filesize is 153 MB (thats about 980 kbps).
To determine what resolution to use I resized it to 512 * 384 (so that b/p*f value is appr. 0.21) and made a first pass with xvid, but the resulting avi was under 150 MB in size. WTF? i thought, undersized although only quant 2 is used? i loaded the stats file with gknot and its b/f*p value was 0.19. so that means that my source is compressible very, very well, doesn't it? (it's a very clean cartoon source) according to the guides i should go for b/f*p values between 0.12 and 0.16 or am i mistaken? such values seem a bit low to me and in gknot they are marked yellow.
so whats your advice? should i go for higher resolution to get into the range between 0.12 and 0.16 or is there a certain threshold that shouldn't be undershot ?

[DJ Bobo]

Well, I'm not really experienced with XviD, but shouldn't you check the AVI after doing the 2nd pass?!

Because 512x384 video saturated already under 150Mb is very rare!

If you're sure the video is saturated, go for a higher resolution, or encode the audio with a higher bitrate to fill the free space (I'll rather go for the second solution).

Don't take this case as a rule, most video need at least 0,2 bit/pixel to achieve decent quality.

[Iznogoud]

I think that GKnot doesn't support Xvid at all so don't trust it in this case, use Xvid's statsreader.

[Iznogoud]

jang0
Get Iago's XviD 2-pass walkthrough from http://nic.dnsalias.com/ if you have trouble with XviD settings. I hear it's very useful document.

[jang0]

Originally posted by DJ Bobo
Well, I'm not really experienced with XviD, but shouldn't you check the AVI after doing the 2nd pass?!

hmm, to make a compressibility check, i thought the video should be compressed with constant quantizer 2.

Don't take this case as a rule, most video need at least 0,2 bit/pixel to achieve decent quality.

Hmm i don't want a general solution, i just want to know what i should do in the case i described above.

Originally posted by Iznogoud
I think that GKnot doesn't support Xvid at all so don't trust it in this case, use Xvid's statsreader.

Hmm, the value given by gknot is the same as calculating:

size of 1st pass video in bytes * 8 / ( number of frames * width * height)

jang0
Get Iago's XviD 2-pass walkthrough from http://nic.dnsalias.com/ if you have trouble with XviD settings. I hear it's very useful document.

Yes, it's useful, i already read it, but it doesn't say much about compressibility/resolution/bitrate.

/edit: hmm, i just realized that i use hmm too often, lol

[Iznogoud]

Hmm...really? :) How big problem is living with the smaller file? If it matters, do like DJBobo says.