how to work out what resolution to use

[rudeboymcc]

hi. i'm trying to encode some movies into Xvid, all to around 700mb. obviosuly they have different running times, and i've found with some that reducing the resolution makes them look better.

is there any way to work out what resolution works best with a length of movie? or shall i just stick with 640 width?

also does it make a difference what monitor i have? my resolution is 1680x1050, so would the movie look better if i make the resolution half of the width? (i.e. 840xsomehting)?

[boombastic]

If you want to do it manually, you can use GordianKnot compressibility test or use an automation tool like ARCalculator or AutoGk.

[rudeboymcc]

i'm using AutoGk but i gave it a 1.5hour DVD source to convert to 700mb xvid and the width it chose was 512. seems very low to me. film is 21grams.

will changing the width make a lot of difference? if it is then i'll start using GordianKnot, although my first, second and third attempts at using it failed miserably.

[boombastic]

I can't tell you if an higher resolution could improve the quality at the same size.To use GordianKnot refer to the xvid guide in the Guide section of doom9.org,it's not so difficult

[woah!]

i have found that my encode of ROTK extended edition at 704x304 returned a compressibility test of 39%. which i thought would give me a terrible result. but after encoding the first disc of 2h 15mins with the 6ch ac3 left intact set as 1400meg total, i was very happy with the results. so i am just more confused aswell now, as i would normally look for at least 70% after testing.

i use AutoGK but with GK Tweaker so i can setup my xvid settings with :

Qpel
Packed Bitstream
2 Consec b-frames
wide search mode 4
Mpeg Matrix

heres a part of the result without sound so i can get the file size down a bit more.

[6/1/2005 1:44:42 PM] Compressibility percentage is: 38.95
[6/1/2005 1:44:42 PM] Using softer resizer.
[6/1/2005 1:44:42 PM] Chosen resolution is: 704x304 ( AR: 2.32 )
[6/1/2005 1:44:42 PM] Predicted comptest value is: 40.41


http://download.mercury.come2store.com/dfdsfjafajeapodfjaefdaef/clip.rar

[Bruce Willis]

The only way to be sure what rez to use, it to look at the xvid and see if there are many artifacts. The higher the rez, the more artifacts there will be..

The best clou which rez to use, is the quality factor (bits per pixel, bpp), indicated in both GK and GSpot. To avoid artifacts, keep it between 0.20 and 0.30.

Of course the bpp is just a guide.. the number depends on the material (amount of action, clean/dirty source) and on your personal favour (how hard you try to find artifacts :)).