Quality settings in AGK

andy

Could someone elaborate about some objective guidelines on using the quot;qualityquot; setting in AGK when encoding to XVid?

I am processing several hundred VOBs that were ripped to HD for playback on my Media Player on a plasma TV over 100mbps ethernet.  Most of the time I just use the 75% quality default and usually get an AVI file about 1.3MB.  This is _wonderful_ as now I have room for three times as many movies!  75% is perfectly acceptable based on my visual tastes.

About 10% of the movies however, come out with an AVI file larger than 2GB when using the 75% quality setting... and the media player can't play past the 2GB mark.  Some just don't compress well at all, and have huge AVI files almost the size of the original VOB, so those I'm just not converting and will leave as VOB.  The others I have to reprocess them with a lower quality setting.  

I'm looking on some guidence on what quality setting should be my quot;floorquot; but there is little guidence in the FAQ.  The only thing in the FAQ is quot;Good quality percentages begin at about 67% (Quantizer 3).quot;  Can someone elaborate?

I've tried using the predefined size of 2GB but most of the time that produces a file that is slightly over 2GB so it is a waste of 7 hours of processing.  Should I use custim size and set it a little below 2GB?  Will I get better quality using custom size if 2GB and the 2-pass encoding than just selecting the quality percentage that gets the file just under 2GB in a single pass?

Also, is a .credits file used when selecting quality encoding mode rather than file size mode?

Hi-

Tough questions those, but I'll try. Of course, quality is subjective, so what one person thinks good quality might not satisfy another.

I and many others usually try and set quant 3 as the floor on quality. The lower the quality percentage and the higher the average quantizer, the more detail is removed from the source. So at some point the result will become too artifact ridden (too smoothed, blocky during action scenes, color smearing, too much mosquito noise around hard edges, that sort of thing). And ordinarily quant 3 is a good cut off point for quality. However, if the source is noisy/grainy, you can often get away with a lower quality percentage, perhaps as low as 50% or so. Film grain works to hide or cover up many problems.

But there's another way to cut the size rather than just lowering the quality percentage, and that's to lower the resolution. In those cases where the size gets too large, you might try and set a fixed width of 640. You mentioned having a Plasma screen, so you're conscious of the fact that if the quality isn't high enough, it'll show on your TV, where it might not on a regular standard interlaced TV screen. I've also got an HDTV, and resolutions like 640x272 or 640x352 look plenty good enough. So you might try that the next time you get one of those over 2 GB results.

Will I get better quality using custom size if 2GB and the 2-pass encoding than just selecting the quality percentage that gets the file just under 2GB in a single pass?

No. But 2-pass encoding does have the advantage of giving it to you for sure in the 2 passes, whereas unless you do some good figuring, trying to hit just under 2 GB using quality mode can possibly result in having to run several passes.

I don't know for sure about credits encoding working in quality mode, but I don't see any reason why it shouldn't.

Credits encoding do work in quality mode, so you get a smaller filesize by using a .credits file in quality mode.

Originally posted by manono
I and many others usually try and set quant 3 as the floor on quality. Understood... but is there a way to know when quantizer 3 is used/notused for sure?  Is that at 67% as implied in the FAQ (which says quot;aboutquot; 67% ... not very specific)?

Originally posted by manono
I've also got an HDTV, and resolutions like 640x272 or 640x352 look plenty good enough. So you might try that the next time you get one of those over 2 GB results.
[/B]

That's the kind of advice I was looking for.  Thanks.  So If 68% gives me a file over 2GB, I should try fixed width of 640 instead of lowering the percentage?

Originally posted by manono
No. But 2-pass encoding does have the advantage of giving it to you for sure in the 2 passes, whereas unless you do some good figuring, trying to hit just under 2 GB using quality mode can possibly result in having to run several passes.
[/B]

Nice in theory, but 3 out of 4 I did that way ended up just sightly _OVER_  2GB.... so I was back to guestimating.

Hi-

... but is there a way to know when quantizer 3 is used/notused for sure?

Back in the old DivX 3.11 days, you divided the ave. quant into 200 and got the percentage figure (200/3=66.67%). So that's where the quant 3=67% came from. But with B-Frames, those figures are no longer exact. However, to get the quants used, open the final .avi in DRF Analyzer and it'll tell you. But remember that B-Frames have higher quants, which depend on the settings (2/1.5/1, I believe, in the case of AutoGK), so don't be alarmed when you see half the quants (or thereabouts) higher than 3. The figures you want are for the P-Frames.

So If 68% gives me a file over 2GB, I should try fixed width of 640 instead of lowering the percentage?

Might be worth a shot. You can get a rough idea of the final size of the lower res .avi compared to the original one by multiplying the original file size by the pixel count of the lower res divided by the pixel count of the original res.

Nice in theory, but 3 out of 4 I did that way ended up just sightly _OVER_ 2GB....  

That's strange. You're sure they were over 2 GB, and not over 2,000 MB, or over 2,000,000 KB? There's that 1,024 thing to consider, you know. 2 GB=2,048 MB=2,097,152 KB.

Originally posted by manono
Nice in theory, but 3 out of 4 I did that way ended up just sightly _OVER_ 2GB....  

That's strange. You're sure they were over 2 GB, and not over 2,000 MB, or over 2,000,000 KB? There's that 1,024 thing to consider, you know. 2 GB=2,048 MB=2,097,152 KB. [/B]

Yup... been doing binary math for over 20 years!  I only figured out it was a 2GB problem when I played back one of the movies and it hung about 30 seconds before the credits started.  That started me hunting and I figured out it was hanging at the 2 gig mark as the file was about 50K over the 2048MB mark.

Last one resulted in a file 2,102 MB

It would be nice if the AGK added to the log the final size of the resulting file... might help in debugging.

I checked the log of the last one done in 2GB mode and it was already reducing size to 608x352.

Cest la vie.

I've resolved to leave a few of them that are long or don't compress well as native VOBs.  Saving Private Ryan is one... reasonable quality results in a 3.5GB Xvid file.... no reasonable amount of compression is going to get that sucker under 2GB!