Is "Re-calculate bitrate if needed" causing a problem?

[Tau]

Hi!

Does anybody know what "Re-calculate bitrate if needed" in GKnot does? I have searched guides and faqs but found only a small note saying I should keep it selected. But what does it do?

I suspect it may cause a weird problem I get when I encode a small file at 1500/2000/2500/3000kbps and the final file size is always identical!

Could anybody kindly give me a hint as to what is going on, please?


Thanks in advance :-)

T.

[manono]

Hi-

One reason that you should keep the Recalculate Bitrate box checked is because of the audio. Before doing it, GKnot doesn't know exactly how much room to allow for it, and the bitrate is based on a rough estimate. After the audio is finished, the bitrate is recalculated to take into account the now known audio file size. There may be other reasons also, but I don't feel like pondering them as your problem has nothing to do with that.

Your problem is the known and simple fact of having maxed out the quality already. That is, after every frame is encoded at quant 2, you can increase the bitrate all you want, but the file size won't budge. If for some reason you really want a larger file size, then increase the resolution, knock off the B-frames, give it a sharper resizer, better quality audio, etc. Perhaps Acaila's sticky on Undersized Files (http://forum.doom9.org/showthread.php?s=&threadid=24584) will help.

[Tau]

Hi!

Thanks for all this information!

Obviously I wasn't trying to get a bigger file :-) but I hoped for better quality. Not being able to do any difference after 500kbps was confusing (n\haven't tried anything lower). You wrote "...after every frame is encoded at quant 2, you can increase the bitrate all you want..." I am aware of the "can't go higher" situation but I know nothing about the "quantity of 2". Could you possibly point me to any article/guide/site where I could read more about this? I have read a lot of stuff but I have never seen this mentioned (or I may have forgotten :-(

Thanks tons :-)

T.

[manono]

Hi-

Obviously I wasn't trying to get a bigger file :-)

Well, you may not have thought you were, but since bitrate is directly correllated with file size, by increasing the bitrate, you increase the file size, and the quality (until you reach quant 2). Quant is the common abbreviation for quantizer (and not quantity). The quant value of a frame determines how much information or detail is removed from the frame, or put another way, how much the frame is compressed. Practically speaking, quant 2 is the best quality (there is a quant 1, but it creates files too large to be useful).

So, if you maxed out the file size, but the quality wasn't to your liking, there could be other reasons for that. Perhaps your source wasn't too good to begin with. Maybe, if from a DVD, it was widescreen letterboxed and not anamorphic. Or maybe your resolution was set too low, or your source was a low resolution .avi. Maybe your desktop color quality was set for 16 bit and not 32 bit. Maybe your video card sucks.

However, in the first post, you mentioned 1500 as being the lowest bitrate after which the file size didn't increase. But in the second post you mentioned that the size didn't increase after 500kbps. It's common to max out the size at 1500, but not at 500, unless your resolution was set quite low (and unless it was a typo). So, if that's the case, you might try your tests again with the resolution set for 640*xxx or something like that. And there could be other factors at work here that I haven't thought of, and you haven't really given us much information to work with (like the .avs, or the logfile if you ran 2 passes in GKnot).

As for more information on quant:

From Doom9's Glossary (http://www.doom9.org/glossary.htm#quantizer):Quantizer

To truly understand this term you'd have to take a course in signal processing. In laymen's terms it means compression factor. The higher this value the more compressed an image is (and therefore a high quantizer means low quality picture and small size whereas low quantizers means high quality picture and larger size).

[Tau]

Hi!

Thanks for your reply :-) I will, check the URL! Thanks.

I did another test with 500 kbps and the size was identical. The .avi files (500-3000kbps) differ only with a few bytes?An example FC compare is here:
00001138: 65 52
00001139: 74 6F
0000113A: 65 43
0000113B: 6C 6F
0000113C: 65 5C
0000113D: 28 73
0000113E: 0A 6F
0000113F: 56 74

My resolution is 672x496. The source is pretty good. My desktop is set to 32bit. My card is nVidia geforce3.
I am using GKnot 0.26, Virtual Dub 1.5.1, NanDub 1.0rc2 and DivXPro 5.0.3. (spyware removed).

I have no idea what is happening. Do you?


Thanks in advance for your kind answer :-)

T.

[manono]

Hi-

You should upgrade to GKnot 0.27 (RipPack and SystemPack). You can leave off installing DivX5, since you have 5.03 already. But that doesn't explain your problem. Assuming you ran the tests through GKnot, you might enclose one of the log files so we can have a look. Because, frankly, I'm stumped. :)

But, since you're still using GKnot 0.26, you might go into VDub and then Video-Compression and make sure you have DivX 5.03 in there. And check to see that you don't have DivX 4.12 there. If they're both there, you might have conflict problems. So, uninstall DivX 4.12, and then reinstall DivX 5.03. You might reinstall DivX 5.03 anyway just to be sure.

[Tau]

Hi!

I tested the thing a bit more and it gets even more confusing.

I have upgraded to GKnot 0.27 (RipPack and SystemPack).
I have checked Virtual Dub and yes, it is using DivX5.

I encoded the file again at 2500kbps. The results were identical (same size as with 500-3000kbps). The I fiddled with "Re-calculate..." and "B-frames" (turned them both off I think) and suddenly the movie encoded at the correct bitrate (size jumped from 47 to 127 MB). But now I am back where I came from since I cannot make THIS size to budge. I am fiddling with bitrate, re-calculate..., B-frames, but nothing happens. The size is again identical.

Bummer.

Any ideas, please?

T.

[Tau]

Hi!

Made a mistake! Very sorry :-( When you told me to check Virtual Dub for possible use of DivX4, I didn't check the job control. I did it now and YOU WERE RIGHT! VDub is using DivX4! At least it says so :-) It puzzles me, because I only have DivX 5.0.3 and possibly also "DivX 3.11 ;-)" installed (GKnot allows mne to choose between DivX311 and DivX503, but I cannot pick up 3.11 in any list so i think it is really not in the system). I checked the system and I cannot find DivX4 anywhere. I have reinstalled DivX 5.0.3 BTW.
I know I could go with other application, such as DVDx, but I really like GKnot and would love to stay with it. That's why i am trying so much to solve this problem. Would you kindly have any tip for removing DivX4 and/or having VDub use my DivX 5.0.3 instead?

Many thanks in advance :-)

T.

[Tau]

Additional information you may find useful. I have checked the *_gnot.log file and found that DivX4 appears twice in here:

###START
Adding this script to C:\PROGRA~1\GORDIA~1\virtualdub\VirtualDub.jobs:

// $job "DivX4 First Pass"
// $input "E:\makrob7(no recalc, bi yes).avs"
// $output "E:\makrob7(no recalc, bi yes)_Movie.avi"
// $state 0
// $start_time 0 0
// $end_time 0 0
// $script
###END

###START
Adding this script to C:\PROGRA~1\GORDIA~1\virtualdub\VirtualDub.jobs:

// $job "DivX4 Second Pass"
// $input "E:\makrob7(no recalc, bi yes).avs"
// $output "E:\makrob7(no recalc, bi yes)_Movie.avi"
// $state 0
// $start_time 0 0
// $end_time 0 0
// $script
###END

I have also searched registry and found DivX4 only in DivXNetworks/DivX4Windows entries.

[manono]

Hi-

Would you kindly have any tip for removing DivX4?

Nope, I never installed it myself. But if it's not listed along with the other codecs, I don't think you have it.

I have checked the *_gnot.log file and found that DivX4 appears twice in here:

That doesn't mean anything. TheWEF never changed that from the old DivX4 days.

What I might suggest is that you do your actual encoding directly in VDub. Use GKnot for cropping, resizing, .avs generation, getting the bitrate, and then open the .avs in VDub and run your 2 passes in there and see if you have any better luck. You can use Doom9's Guide (http://www.doom9.org/divx5-vdub.htm). Or maybe use the DivX.com Guide (http://www.divx.com/support/divx/guide.php).

[jggimi]

...because I only have DivX 5.0.3 ...GKnot 0.27 does not support 5.03 or above, only DivX 3.11 or DivX 5.02. You can use GKnot to create .avs files if you have 5.03, but you cannot use it to encode, and must encode with Vdub manually (or with Jonny's DivX5 Enc tool).

[Tau]

Hi!

I have made some more tests and it seems the problem was GKnot not cooperating with the new DivX 5.0.3. It's a pitty, since GKnot works so nice with 5.0.2. I am using it to do the .avs and then I go to VDub and NDub for video compression and audio mux. This works well, even with the tricky 5.0.3.
I'd like to thank to all who replied for their kind help. I wouldn't be able to get thru this without you. Thanks :-)
T.