B-frames may not be all that good!

[ToMmY]

I have done a few tests and i found out something really interesting:
From the 3 "working" pro features i used every combination.

---GMC seems to work ok without any artifacts but it doesnt seem
to affect quality. I use it anyway!
---Quarter pixel works ok for me (up till now) without any artifacts.
On the contrary, it boost quality. For example: face closeups.
Faces now have less blocks AND get impresivly better detail. It is
like the detail XviD gives us (and even better)but without the blocks!. For me it is the best of the 3 features and if you dont get any artifacts it is a must use!
Note: i used 1500kbps and 704X... and QP worked great!. i dont know
about the fact that it works best on 1/4 of the image!
---And now the "pain in the ..." AKA b-frames! I think that they are
both good and bad!. Some frames (or maybe all) get better detail but
the problem is that now i get blocks! LOTS OF BLOCKS! big and ugly!
There are frames like close ups where i dont see that problem but
on fast scenes with solid color (like an avalance going down a
mountain) lots of blocks appear + the fact that trying to give more
detail the codec creates blocks with colors(like green or yellow)
that seem realy ugly (eg a statue in a mysty area).

---When I use QP AND B-frames i get the same ugly blocks that the
b-frames generate but this time the quality boost of QP aint that
impressive. It is just noticable!

---So: i get the best quality when i use QP+GMC! b-frames always
create blocks and DOWNGRADE QPs quality!!

I would like to post some pictures but i have the following problems:
1. i dont know how to save an image with vdub(i use vdub to compare
frames)
2. i dont know how to post a jpg that i have in my HDD (should i upload it somewhere and then link it? how?where?details please!)

I would also like to report AGAIN the 1 and 2 frame problem that divX5 has + the fact that it is realy annoying when i try to find a frame with vdub and the frames get screwed! i may press the backward key and see a frame that is 50 frames back! SO STUPID. Couldnt they just avoid it?

What do you think about the above?

Thanks for your patience!
I am looking forward to hearing from ya!

[NetSoerfer]

at least for your second question, the answer should be rather easy...

just click on "browse" in the "attach file" area and search for the jpg on your harddisc. i think you can only attach one file, so maybe you should compress more files in one zip and post that one.

btw, the moderators will have to approve the file before it becomes visible under your post.

soerfer

[gregor7777]

I'd like to see the results as I don't have the time to do a comparison for myself.

I've used B-Frames and GMC together for the movies I've done so far with divx 5 and find the quality to be about the same if not slightly better in scenes where the camera is panning around a large area, such as the intro in Braveheart, than what was with divx4. But I can see what you mean with the closeups on faces. It is blockier than my older movies.

[ToMmY]

OK!
here are some sample frames
i also include a notes.txt with info
the file is 600kb sorry
it has jpg sample frames
Im waiting your opinions.


Hope the administrators will not filter it!

[-h]

Just to make it clear, DivX5 actually doubles the quantizer for B-frames. That is, if the previous frame's quantizer was 4, the current B-frame's quantizer would be 8. That's how DivX5 works, and there's no way around it.

It's not entirely bad though. The B-frame-induced blocks should only appear every second frame, so if you step through the frames in VDub, this should be apparent. Watching at full speed, however, it's not all that easy to notice the difference.

Allowing the user to specify how heavily B-frames should be quantized would have been a better method, imho.

-h

[timeToy]

There is no settings in the GUI for changing the B frame Quantizer multiplier but you can do it in the registry :
HKEY_CURRENT_USER\Software\DivXNetworks\DivX4Windows
Key "Bidir quant multiplier" by default it's set at 8192 and the Q multiplier is 2 so Qx=Bidir quant multiplier/4096

Bidir quant multiplier=8192 Qx=2.00
Bidir quant multiplier=7168 Qx=1.75
Bidir quant multiplier=6144 Qx=1.50
Bidir quant multiplier=5120 Qx=1.25
Bidir quant multiplier=4096 Qx=1.00

BTW
Messing with the B frame Quantizer Multiplier can raise the quality but also the bitrate...

[ToMmY]

So what do you really think about B-frames?
Should we "always" use them?
I think my frames show that the quality is "poor" using b-frames, but they are supposed to give "better" quality!
Could b-frames be a "trick"? (they might have thought: lets make b-frames worse -> this way we can save bitrate for the rest of the frames! -> so as to increase bitrate -> and make divx5 look like the best codec!)
B-frames were supposed to be "a dream come true" regarding quality.
What do you think of QP? doesnt it give quite a quality boost?

All the above have to do with frames comparisson not how the movie looks! I just want to belive that better frames=better movie!

By the way :timeToy that is a nasty little tweak! Great!

[Doom9]

better frames = better movie is so not true, especially when features like b-frames, gmc, qpel or psy stuff comes into play.

But I was told to play with the quantizers when using b-frames (never had time to actually do it:( , try a min quantizer of 9 or 10 and compare again.. maybe you'll see a difference

[madoka]

My personal experience with B-frames so far has been pleasant. There's no noticable (IMHO) quality loss at a given bit rate, but it saves 10%~30% compared to without B-frames. Playback is a bit more problematic, however. My laptop can't quite handle decoding at times with anime rips, while movies seems fine. Probably has to do with the amount of postprcessing required.

[Ned]

Based on the samples posted in this thread, quarter pel alone looks best followed by the non pro frame. The rest look like trash in still frames (maybe it's not noticeable in motion). GMC seems to have slight to no impact on quality.

Divx5 is looking like hacked junk to be honest. Most of the new features don't appear to work or cause more artifacting than they are worth. The huge increase in cpu playback requirements isn't exactly a great feature. A p2 400 can play pretty much anything made with divx 3.11a but divx5 with B frames needs a 1ghz+? I think we should just focus on Xvid instead of this hackjob/money grabber DXN product.

[ToMmY]

Something else i would like to mention:
someone (sorry i dont remember who!) gave us a little file that would allow divx4 to work together with divx5!
I have installed it. Could it cause that problems with "my" B-frames?
I mean... could it have screwed up my divx5 installation?

[A_Pleite]

@ned:

Divx5 isn´t that bad. Capturing with divx5 is better than with xvid, because divx5 has preprocessing and resizing in the codec - I can send the yuvu-signal directly to the codec and make it filter the pictures. That speeds up the capturing -> less dropped frames, bigger resolution, better filtering -> better quality. Besides this, divx5´s quality is really good(/size is small) with constant-quality(which I use for capturing).

@ ToMmY:

QPel gives me shitframes (don´t know why), B-frames give good quality. Encoding with VDub I can see that b-frames only use 1/4 - 1/10 of the size of p-frames.

[theReal]

@ Tommy
I have also installed both codecs and it works fine. I only reinstalled DivX 4.12 because I can't capture to Divx 5 - VDub crashes after only a few seconds (that was before I had both codecs installed as well as after...).

I don't see any quality loss with b-frames. At a given bitrate, b-frames are smaller than I and P-frames - but that also means every other frame is bigger than it would be possible with other codecs.
I think if the quality based size with b-frames is ~25% lower, I can lower the bitrate for a bitrate-based encoding by about 15-20% and get better quality in the end (or at least the same quality).

I have never heard that Divx 5 was advertised to have better quality at a quantizer 2 setting because of b-frames. It was said to allow smaller files at the same quality, tho.

In my opinion, with or without b-frames, the picture is a little sharper with Divx 5 than with divx 4 (which still had been a major drawback compared to Nandub)

[jack-gal]

My experience with divx 5.0 has been very good so far.
In my tests (a 3 min movie from DVD, in both 1300kbits/s and 700kbits/s), b-frames has a major impact on quality. I like it :) !
GMC doesn't seem to change something, i use it anyway.
I found that Qpel has a very little impact on quality, but it drasticaly slows down encoding, and my P3-750 can't handle decoding at max perf. settings :(. I prefer to use GMC and B-Frames with max. postprocessing setting, than Qpel with medium.
However, filesize predictability is impressive. I get only 2~3 Ko differences between Bframes, Bframes + GMC, Bframes + GMC + Qpel, on a 15Mo file. But I think I've been very lucky ;) !
So, i was not enthusiasm for this new codec at first time, but after trying it and testing it, i can't go back to divx 4.12 !

jack'gal

PS: i'm fench, sorry for my bad english !!

[veets]

Your English is pretty good for a Fench person (better than all the other people I know from Fance)

[hippoth]

@timeToy

can you explain exactly whats the effect of your little "tweak" with the B frame Quantizer multiplier (what is it?)...I don´t understand what it effects...increasing quality?

thanks for answering :o)