Greatly undersized encoding

[Polarbear]

Hello all,

Just started using Xvid, and with the Xvid build that came with the Gknot 1.03 Codec Pack using Qpel, VHQ-4 and other settings, the final video + VBR audio was about 150 megs undersize when I opted for 1.45 gigs. I know the size prediction is not as accurate as that of Divx's, but 150 megs off from 1.45gigs was a bit too much. Any solution / work-around /suggestion that you experts can provide for this simple matter?

Thanx in advance,
-Polarbear

[manono]

Hi-

I think that, if anything, the XviD file size prediction is more accurate than DivX. Did you run a compression test in GKnot before encoding to make sure that you could even reach the desired file size? The chances are good that you maxed out the file size. Read Acaila's Sticky on Undersized Files (http://forum.doom9.org/showthread.php?s=&threadid=24584) to see if it applies.

And you should probably upgrade GKnot to 0.28.5.

[Koepi]

Originally posted by Polarbear
Just started using Xvid[...]I know the size prediction is not as accurate as that of Divx's[...]

*rotfl* you're sure, right? >:)

Koepi

[ffroms]

@manono-Polarbear said that he used GKnot Pack (that's codec and filters pack).

@Polarbear-Try doing comp. test without B-frame and set VHQ 0 or 1 (for 1.45 gigs you don't need to use any higher VHQ). Xvid can reach file size with error of 500kb unlike divx with error of few MB's.

FFS

[Polarbear]

Thanx guys for the help!

I had time to do 2 Xvid encodings of 2 different films during these day and half. The primary differences were the use of VHQ - 4 and VHQ - 2. (Still trying to get over the fact of going at ~5fps on a relatively fast AMD 2600+ system with VHQ - 4.) Right, I know I should have done the testing with the identical film, but I simply do not have the CPU power to spare at this time.

VHQ - 4 turned out 150 meg+ undersized, while VHQ - 2 hit the size mark very nicely. Why is that the case? (Brief description will be fine for the non-technical me if an obvious explanation is there.)

Since we're at it, I have three questions, all fairly suggestive and of course, not dealing with extreme cases (ie., 2 hours of movie where random images are placed on screen for every frame):

1) Are there drastic quality differences between VHQ 0, 1, and 2? Especially in my case of always encoding at fairly high bitrate of 1700 kBit/s (1490+ megs)?

2) I personally cannot see the difference on my monitor between Divx 5.05 (GMC, Bi-dir.) encoding of a film and that of Xvid (Qpel, VHQ-2, and other 'stuff') encoding, of almost exact sized film. Maybe I'm basically blind compared to you guys who seem to be able to see the pixel differences between various encodings down to individual RGB variations, but in GENERAL, in such cases, is the Xvid higher in quality then that of Divx 5.05? Two reasons for my asking such a question: a) Eventhough I cannot see the difference right now, I will very likely replay these movies on HDTV or other high definition displays, when I can afford one of those things (year 3060 or something) b) I cannot spare the CPU resources on my ONLY computer (YIKES!!) or afford to build a 60 terraflop system for my encoding hobby.

3) Should I encode at .260 bits/(pixel * frame), though at slightly higher width x height or opt for .300 bits/(pixel * frame) and at a lower width x height? And is it okay to go 'red' in the zooms? With some movies, at 640 x 272, I am already at 100% H-Zoom and at .400 bits/(pixel * frame). I wish to keep the file size of 1490 megs.


Thanx again, guys. You guys are great!

Cheers,
-Polarbear
PS: Sorry Koepi about my ignorant comment...there's nothing I can back that up with. I only have that perception from the threads that I read in this forum.

[K_R]

Since you mentioned your intention of playing on HDTV in the future, you could try encoding anamorphic, ie. resize on playback (discussed in other threads). That should help you hit your filesize desires.

[Imperial Llama]

Originally posted by Polarbear
VHQ - 4 turned out 150 meg+ undersized, while VHQ - 2 hit the size mark very nicely. Why is that the case? (Brief description will be fine for the non-technical me if an obvious explanation is there.)

Some movies require more bits then others. Read the "undersized files" thread that manono provide a link to.

1) Are there drastic quality differences between VHQ 0, 1, and 2? Especially in my case of always encoding at fairly high bitrate of 1700 kBit/s (1490+ megs)?

Using VHQ should theoretically always result in superior quality. You should do some tests yourself to see if you notice any differences or if you think the improvement was worth the extra encoding time.

in GENERAL, in such cases, is the Xvid higher in quality then that of Divx 5.05?

If you understand what you are doing then the results should be quite close. In my limited testing XviD has the edge but you should do some tests yourself to see which you like best. Asking this question in the DivX forum would have probably got you the opposite answer. ;)

3) Should I encode at .260 bits/(pixel * frame), though at slightly higher width x height or opt for .300 bits/(pixel * frame) and at a lower width x height?

It depends on what you are encoding, the bitrate you are going to use and your personal preferences. Doing some test encodes will help you decide.

And is it okay to go 'red' in the zooms? With some movies, at 640 x 272, I am already at 100% H-Zoom and at .400 bits/(pixel * frame).

It won't cause any technical problems but I advise against it due to the fact it often result in bigger file size for little or no quality gain. This is really a Gordian Knot question so you will probably find more information in the appropriate forum.

I wish to keep the file size of 1490 megs.

Reading up on undersized files should help you understand why stubbornly insisting on a minimum file size is pointless. There are ways to force the encoder to waste more bits and therefore producing a bigger file, but the quality may end up being worse. Use the spare space for something else.

*edit* Changing the quant type, as suggested by sysKin below, will probably increase the quality and is not a waste of space.

I have suggested that you do some testing yourself and I know this is time consuming but it really is the best way to understand how different settings affect the quality. You don't need to do encode a complete movie for your tests to produce helpful results.

[Herske]

Now the question is how compressible are the movies you are encoding?

When I encoded for the first time "PANIC ROOM" and "FROM HELL" I hardly resisted the impulse to come screaming "bug bug" :D (those movies are ~2h each and fit nicely in 300-350 MB)

[sysKin]

XviD and DivX will always have more or less similar quality, because they implement the same mpeg-4 standard and they do that at decent level.
If you want to see a difference between them, especially at such high bitrate, you should make XviD use mpeg quant - you actually never said if you used it, but if you haven't seen the obviuos sharpness of xvid - you probably haven't. If you do some very-high-bitrate encodings you can also try mpeg-custom and use some high-bitrate matrices (as discussed in other threads). It will prevent undersizes and will improve quality when bits are available.

Also, it seems you're using very low resolution. If you're aiming at 2 cds, I see no reason to go below 704x resolution for an average movie. I've never went below 688x for one cd and I'm very happy about it. You should usually use sharp and very sharp resizers - they just look very good imho.

After doing all that, the technological edge XviD has might be more visible.

As for VHQ - you don't have to use it of course. VHQ > 0 is a feature that gives better quality, as opposed to "VHQ = 0 being a feature that gives better speed". VHQ=0 still gives higher PSNR than DivX5 has.

Regards,
Radek

[HarryM]

Originally posted by Herske
Now the question is how compressible are the movies you are encoding?

When I encoded for the first time "PANIC ROOM" and "FROM HELL" I hardly resisted the impulse to come screaming "bug bug" :D (those movies are ~2h each and fit nicely in 300-350 MB)

Movie 'Panic Room' has a very gooood compressibility. But many another movies dont.