MeguI undersizing

[zacharias]

hey.
i dont know if this is the best place[thread] to pose may question, but here goes:

i'm kinda noob on these matters, but i use Megui (and my Avisynth verson is 2.5.8.5) for doing my DVD bacups and more recently my BR backups, quality overal is good, but one thing has been haunting me down for ages: files sometimes turn out to be undersized. and it pisses me off. simply dont know what else to do.

ive recently tried to do a BRRip that turned out to be undersized. here are the specs from gspot after muxing:
File Size ..........: 1,454,747,648
Video Length .......: 1:32:07
Video Codec Code ...: XVID
Video Bitrate ......: 1712
Resolution .........: 720x400
Aspect Ratio .......: 1.800
Framerate ..........: 23.976
Audio Codec Name ...: 0x2000 (Dolby AC3) AC3
Audio Bitrate ......: 384
Channels ...........: 6
Sampling Rate ......: 48000

ive recently found a topic on undersizing in doom9 (http://forum.doom9.org/showthread.php?t=24584) forum, that pointed out a possible reason for undersizing and oversizing files.

here's what got my attention:

1. Overflow treatment values tweaking
These settings are used during the second pass and tell the bitrate control which strength it can use to adjust the bitrate. Higher values allow him to be more efficient and to balance these Q1 frames.
So... recommended values are ("Encoding type" > Two-pass - 2nd pass > "more..."):
- overflow control strength: try 10 or 20
- Max overflow improvement: try 10 or 20
- Max overflow degradation: try 10 or 20

You'll get a correct final file size.

now, im really lost as i mentioned, because sum files turn undersized (most of them if i choose 1/3 dvd size fr lengths of over 90min) and others dont (if i choose 1/4 DVDsize). dont get me wrong but some 1/3 dvdsize turned out to be ok.

back to the point, here are my Main and Advanced configs

http://img337.imageshack.us/img337/1412/mainm.png

http://img691.imageshack.us/img691/7287/advancedk.png

i really dont know if the problem lies here, but i think i am. im out of possibilities.
hope you guys know how help me out.

many thanks in advanced.
kudos

[zacharias]

any thoughts?

[Guest]

1873 * video length / 8 -> 1,294,008,875

Your file size is 1,454,747,648

So how is that an undersize?

Please give your full analysis.

[foxyshadis]

Video bitrate's only 1712 though, the remainder comes from the AC3.

First step is to look at the log and see what the average q is. If it's very low for I & P frames, 2-3, switch to a custom quant matrix. You're hitting the maximum possible size. 6of9 is ok (allows xvid to use fractional quants), MeGUI should come with a lot of other good ones.

Actually first watch a bit of the movie and see if you think it even needs more space. If not, why bother re-encoding?

[zacharias]

Video bitrate's only 1712 though, the remainder comes from the AC3.

First step is to look at the log and see what the average q is. If it's very low for I & P frames, 2-3, switch to a custom quant matrix. You're hitting the maximum possible size. 6of9 is ok (allows xvid to use fractional quants), MeGUI should come with a lot of other good ones.

Actually first watch a bit of the movie and see if you think it even needs more space. If not, why bother re-encoding?

i tend to encode using AFR sizing. that why. i wanna use that to encode, even thoug as i stated, the qualit is supperb. but it keeps undersizing.
kudos

[foxyshadis]

If you don't understand the technical reasons why it undersizes, then use a tool like MeGUI that will handle matrices and settings for you for optimum quality, or accept that the undersizing isn't going to matter if it looks good enough. Using scene standards is pointless if you're just going to keep them all on your hard drive or something other than DVDs.

[zacharias]

If you don't understand the technical reasons why it undersizes, then use a tool like MeGUI that will handle matrices and settings for you for optimum quality, or accept that the undersizing isn't going to matter if it looks good enough. Using scene standards is pointless if you're just going to keep them all on your hard drive or something other than DVDs.

im not simply backing it up ;)
as u may assume i wanna use scene output sizes. i just want a costum standard config/setup that allows me to back up movies as good as avidemux or gk, in other words, i wanna use megui without having no worries wotso ever concerning undersizing, that happens only with megui and (back in the day when i used it) AGK.
kudos

[Inspector.Gadget]

Undersizing, if not due to a bug, is irrelevant to quality. It reflects saturation. That's the point. "As good as" is independent from size.

[zacharias]

Undersizing, if not due to a bug, is irrelevant to quality. It reflects saturation. That's the point. "As good as" is independent from size.

well, but as stated before m8, i want quality reflected in determined scene sizes.
kudos

[Inspector.Gadget]

Did you skip over the last two responding posts? Size does not reflect quality once you've saturated the codec. That's why foxyshadis is talking about matrices.

[Sharktooth]

If you absolutely need to get an exact filesize, first use a high bitrate matrix.
If your playback device doesnt support custom matrices, then you can set Min I-P-B frame quintizers -> all to 1 and/or

Overflow control strength ->10 or 20
Max Overflow improvment ->10 or 20
Max Overflow degradation ->10 or 20