Qpel ?

[fredthemasterofpuppets]

Well, is Qpel really useful ?
does it really improve encoding quality ???

In fact, I'd like to know what is the real purpose of Qpel and in what way it should improve quality ?

thanks !

[manono]

Hi-

Here's a Quote about Q-Pel from the DivX Help Guide (http://www.divx.com/support/divx/guide.php) at Divx.com:

As explained in the "B-frames" summary, data is reduced when the difference between two frames (prediction error) is transmitted instead of the entire image being sent. The difference in a successive frames composition is generally computed on a macroblock-by-macroblock basis (16x16 pels) or on a block by block basis (8x8 pels). For example, a part of an image located in a block at grid location (1,1) may move to grid location (1,2) in the next frame. As you may realize an image in one block will likely need more accuracy than just the ability to move on a limited block by block basis with an accuracy that is limited to an integer pixel unit (1,1). DivX has increased the previous accuracy of using a half pel (1.5, 1.5) to include the ability of using "Quarter Pel" (1.25, 1.75) accuracy with the Codec release. Quarter Pel performs a specific filtering on each block to produce a virtual block that should represent how the original block should appear if it is moved a 1/4 of a pixel unit. So, do you know any more than you did before? Doom9 says in his guide:.In my tests quarter pixels (QPel motion estimation) didn't result in a visible quality improvement and initially caused a lot of strange artifacts so I wouldn't suggest using it.
I think the consensus around here is it's buggy and shouldn't be used. I know I don't use it

[fredthemasterofpuppets]

well, thanks, but I had already read the divx help guide, and I didn't exactly understand, why it should improve quality according to the explanation.
but if Doom9 made several tests and the results were bad, I won't use it, but I was just wondering, for I never used Qpel before.

[drizztcanrender]

Also q-pel dramatically increases the cpu needed for decoding.I wouldn't suggest it for pcs with slow cpu's.

[cordraconis]

Hey! That is nice to know!

I convert my Rips to DivX 5.02, and 1 cd if I use Lame-ABR, and 2 Cd's if It has AC-3 soundtrack. (Depends on the movie dough ):)

I used Q-pel for a few movies, but i found no difference, so now I don't use it any more.

But a friend of mine tried to play it on his AMD 350 Mhz, and my rips (DivX 5.02), don't play well. (jerky and slow, with stuttering sound).

The 5.02 codec doesn't play either 3.11 or 5.x pics like it should be, even when I turned all post-processing off. Only the 3.11 Alpha codec is reasonable.

But I haven't tried my latest 5.02 (without Q-pel) on such a system ... Maybe it could work, if it is like you said that Q-pel raises the requirements for playback.

Anyone has some experience on "minimum system requirements" for DivX 5.02 (with different settings and soundtracks)????

For example; I converted the 2 CD L.o.R divx to a 1 CD-rip with mono sound for a friend of mine, (with limited diskspace, since I consider a 1 CD-Rip for Lord of The Ring as Blasphemy :D ), and he played it on his Pentium III 500 without any probs. Then again, I have personally whitnessed my 2 CD AC-3 DivX 5.02 stuttering on a Pentium III 700 Mhz. (It was a Compaq laptop, dough ;) ).

So, any minimum requirements? Comments would be appreciated!

TIA

Cordraconis

[manono]

Hi-

You combine a hi-res .avi with VBR sound and separate subs, and you'll need a decent CPU. I've seen an Athlon 1 GHZ CPU choke on panning and scrolling scenes in a 640x480 movie. However, I think the DivX5.02 decoder is more CPU intensive than ffdshow (http://www.doom9.org/Soft21/Filters/ffdshow-20020617.exe). So you might tell your friend to try it with no post processing. But it still might not be good enough for an AMD 350 to play full screen.