I can't get the file size I want, not a single time (including encoding reports)

[bjfacca]

I use Gordian Knot for about a month now and I encoded about 10 movies with it, It's a great tool. My only problem is that I can never predict the file size I will get doing Divx 5.0.1 2-pass encodes. I always get a file that it's *a lot* smaller than the value I put in Gknot's calc.
I know about movies that reach the maximum bits per frame at a certain bitrate and it happened to me a couple of times, but thats not the case, except maybe for a couple of them. Below are some info about encodings I did using Gknot 0.23 with Vdub 1.4.10 (original ver).
The value before (Gknot) is the average bitrate calculated by gknot and before (used) is the bitrate I've used (duh). Some info is missing because I forgot to write it donw at the time of the encode. All movies are in 640xXXX, mostly 272 for anamorphic and 480 for non anamorphic.
All movie sizes do not include sound.
My PC is an Athlon XP 1700+, 256 DDR on a Soyo Dragon +, 2x 40GB Samsung in RAID mode 0
*All* of them are set to 2x 700mb CD or 2x 650mb CD.

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don't say a word
1618 (Gknot), 1650 (used) -> 761mb <- What the hell was that?

same movie/settings only with a higher bitrate
1618 (Gknot), 2700 (used) -> encoding right now, I'll post is later if you're interested

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swordfish
1904 kbps (Gknot) -> 2000 (used) = 1,09gb

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vertical limit
1618 kbps (Gknot) -> 1650 kbps (used) = 761mb

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15 minutes
Used Gknot's IVTC
1450 kbps (Gknot), 1450 (used) -> 1,19gb
sharp bicubic filter
5:43 encoding time

same movie using Decomb and a higher bitrate
1450 kbps (Gknot), 1520 (used) -> 1,17gb looks like its "saturated"
sharp bicubic

same movie using Decomb and Bilinear filter
1450 kbps -> 1,09gb
5:10 encoding time

---------------------------------------------

final fantasy:
force film was done
no IVTC
1724 kbps (Gknot), 1800 (used)-> 1,01gb
sharp bicubic
3:40 encoding time

same movie/settings only with a higher bitrate
1724 kbps (Gknot), 2000 (used)-> 1,01gb "saturated" for sure.

--------------------------------------------

6th day
force film was done
no IVTC
1427 (Gknot), 1500 (used) -> 1,06gb
sharp bicubic
3:50 encoding time

same movie/settings only with a higher bitrate
1427 (Gknot), 1700 (used) -> 1,10gb

----------------------

the mummy returns
force film was done
no ivtc
1365 (Gknot), 1400 (used) -> 1,19gb
sharp bicubic
4:34 encoding time

----------------------

Any thoughts on why is this happening and what cna be done?

Sory for my bad english, I live in brazil.

Bruno

[jggimi]

Your English is perfect!

This is only a guess, but, since all of your encodes were done at "640 x ____" I am guessing that 1) you have skipped the examination of bits/(pixel*frame) loading estimates, and 2) you don't do compressability tests.

Jonny has created both methodologies and tools for doing compression tests for DivX5. He's also done a series of tests to determine what loading factors produce consistent size results. There's a variety of threads on this subject in the DivX5 Encoding (http://forum.doom9.org/forumdisplay.php?s=&forumid=56) forum.

[bjfacca]

About my english, thanks, it's good to know that it's getting better.

This is only a guess, but, since all of your encodes were done at "640 x ____" I am guessing that 1) you have skipped the examination of bits/(pixel*frame) loading estimates, and 2) you don't do compressability tests.

I tried different resolutions before 640x___ but that was when I used flask and xmpeg, you guessed right, I don't pay attention at the bits/(pixel*frame) numbers and I don't do compressibility tests, actually I don't know much about these, like how much bits/pixel in a frame would take to "saturate it".

thanks
bruno

[Acaila]

Please read my sticky (http://forum.doom9.org/showthread.php?s=&threadid=24584), and try to use a compressibility test next time.

I can already tell you that 3 out of 4 movies will be undersized if you use the following together:
- 640 resolution
- B-frames
- 2x700MB CD's
- Any audio transcode instead of the 6-ch AC3.

how much bits/pixel in a frame would take to "saturate it".
I usually find that value quite UNinforming. Different movies require different values to look good. Compressibility is more important.

[bjfacca]

Originally posted by Acaila
Please read my sticky (http://forum.doom9.org/showthread.php?s=&threadid=24584), and try to use a compressibility test next time.

I read your sticky before starting this thread, it was very informative and helped me to understand the factors that make a movie more or less compressible.

thanks
bruno