Looks like I just found a possible way (maybe?). I just downloaded the latest CVS of mplayer (which includes mencoder) and compiled under cygwin. Looks like all rate control code is in a file called ratecontrol.c . Maybe we could change it for our purposes, doesn't look so hard to understand. Anyone with C knowledge is invited!

Aha! Now you're talking VM.
What did I tell you? This guy is a genious!
I'm just sad because I don't know C. That is I don't know any language but pascal, and that was a looooong time ago...
Any volunteers?
Cheers

__________________
Rui

Yeah, but Pascal is more English, while C/C++ is Martian .. "take me to your
leader, ..'Bush?' .."

-vhelp

This function holds the key:
This finds the quantisizer for 1pass vbr for
If we add the line in blue (not originally in the code), mencoder starts encoding with fixed quantisizer 8. (of course, I did this just to test) So it's only a matter to understand how it works and use a fixed quantisizer unless predicted filesize is too big. We'll get there.

I found ou that if you set the parameter vqscale=x in the commandline, you will receive a linear Q curve! BUT very fast blocky pictures on dark areas at lower vqscale's like 3.
IF you set vqmin=500 and vqmax=5000 including a vbitrate=xxxx (was it that command for bitrate? Im at work now) the blocks at dark scenes are almost away BUT on the other hand blocks will appear on fast moving scenes! By this - said without determine the vqscale in the line - the Q curve isn't constant anymore BUT more adaptive to the scene contend which results in less blocks in underwater scenes. But to avoid on the other hand the blocks in moving parts, you have at least to set a vqbitrate=3000.

By this BTW I obtain an encoding-speed of 25fps (my system), means realtime including Avisynth on a 25fps 704x576 stream even a little bit faster than CCE.

But thats all for regular DVD encodings, not KDVD to put 2-3 Moves on one DVD-R Media.

Inc.

PS: So it would be interesting to see in what quality and what vbitrate value does fit the LOTR II SpecialEdition on one DVD-R including AC3. But I don't have that special Edition on my own, so I can't test it.

I have a different opinion: you want constant quality within the bitrate limits. Constant quality can not be the same as constant quantizer if you want to respect those limits. More important than the filesize is the bitrate specification.

What seems to be difficult is having a vqsquish-like parameter for bitrate, using the best quantizer but trying to keep the frame within the bitrate boundaries. And that would mean change the quantizer on a bitrate criteria, not a filesize criteria.

EDIT: From my post above, taken from a mailing list:
Solution seems to have been found!

vqcomp=0 -> vrc_eq=tex^0=1 -> constant bitrate
vqcomp=1 -> vrc_eq=tex^1=tex -> constant quality

And this parameter seems to respect the bitrate, not like vqscale. Could someone test it, please?

Bilu

Sorry, but this is about the same thing I said.
No it's not. Unless you want to use 2-pass VBR. But you can't have a good One Pass VBR mode that respects some average bitrate. Because you'll see something like I said: the encoder can vary the bitrate for a while, but it will get back to the average, ruining the picture, even if the high action is still happening. You can't have good quality and completelly predictable file size in 1 Pass Quality Based, it's impossible. So you must be thinking : why you want that anyway? Because this way I can use prediction (my CCE method) and do 1 pass, what is much faster than 2-pass VBR and has a accuracy of about 3% with every encoder, enough for most people.
But CBR is always known to produce bad quality in high action scenes and wast bitrate in low action scenes... Why would anyone want that?

Now this is interesting. I'll test it.

I was referring to respecting minimum and maximum bitrates to be DVD compliant.

IMHO this is even more important than filesize.

Bilu

I tested... But it doesn't woked as I expected. There are many places where this did not work, but the worst example is one high motion scene that got the quantisizer 30 to achive bitrates around 600, while I specified the max 2500.
Maybe we should try some other rate control equations...

I agree with you, but I think DVD standard does not define a minimmum bitrate... Actually I never got bitrate beyond 9800 using fixed quantisizer. I guess it's more problematic if we're trying to do a KSVCD/KVCD...
I am playing with vqcomp=1 and different rate controls.

This will work:

vrc_minrate=300
vrc_maxrate=2500
vbitrate=2500
vqsquish=1
vqcomp=1
vrc_eq=tex

Unlike it seems, it won't produce 2500 CBR, but will make almost what I want, that would be use quantisizer 2 unless bitrate needed is too high. In this case, use the lowest quantisizer possible to don't go over the maximmum (2500). Seems like using maxrate equal to bitrate makes the encoder don't care about average bitrate (what we want after all)

EDIT: I just have no idea how to rise the quantisizer used when Maximum is not exceeded. I've tried mbqmin and vqmin, but looks like after some time it goes to 2 again. Also I can't use fractional values...

Hi guys,
Though not having posted anything yet I've been trying VM's last post arguments except for vqcomp=1 & vrc_eq=tex.
Didn't find a way to constrain bitrate and try maintaining quality as constant as possible...
Damn, if you find a way to this let me know .
Maybe the next day one German guy we all know very well has come up with a nice GUI to it too
Cheers

__________________
Rui

What I posted will work, but the final size will be unpredictable. And I don't know yet how to lower the constant-when-possible quality to have less filesize.
Also lower bitrate doesn't seem to be working, but this is easy to understand, looks like even using quantisizer 2 (tjhe lowest possible) some scenes fall below the minimmum bitrate.

@vmesquita

Maybe using vqcomp=0 (without messing with the default vrc_eq) will do the trick. After all, it will aim at constant bitrate - so if you equal the average and maximum quantizer it will try the keep at the lowest possible quantizer for that bitrate. And filesize will be more predictable because bitrate will be more constant

EDIT: Rewriting this post, see if this is what you want:

vrc_maxrate = vbitrate -> average will be the maximum bitrate (nice idea VM );
vqcomp=0 -> tries to keep as close to bitrate as possible;

Seems to me that vqcomp=1 tries to keep as close to the original quality as possible but then there is the matter of how is Mencoder perceiving quality from a frame. Mencoder may find a high-motion scene to be low quality and decrease the bitrate (that's probably what happened to VM in a earlier post).

With vqcomp=0 it will try to encode in the closest possible way to the average bitrate regardless of the perceived quality, so using vrc_maxrate = vbitrate together with vqcomp=0 serves our purposes I think

Really cool is the fact that it won't care about texture complexity - just fit it all into maximum bitrate!

Someone willing to try?

vrc_minrate=300
vrc_maxrate=2500
vbitrate=2500
vqsquish=1

vqcomp=0 OR vrc_eq=1 (if you use a vrc_eq without qComp, the vqcomp becomes irrelevant)

EDIT2: vqmin and mbqmin already default to 2, so you don't need to mess with this parameter. If a frame gets less than 2500 at quantizer 2, it won't change to quantizer 1 just to fill the avg bitrate request.

EDIT3: Since this means:

- Lowest possible quantizers;
- respected maximum bitrate;

I don't know what kind of advantages a 2-pass encoding process would bring in this case. None, I think

Just calc the average/maximum bitrate and you're all set!
You won't even need prediction methods

It's like a HiQ CBR


Bilu

vqsquish=1 ?

If using vqcomp=0 and vbitrate=vrc_maxrate there is a small chance that sometimes it goes over the maximum bitrate to fit the average - it depends on how much the vrc_maxrate is respected when using vqsquish=1.

If so we have to use vqsquish=0.

vqsquish=<0,1>
specify how to keep the quantizer between qmin and qmax (pass 1/2):
0 use clipping
1 use a nice differentiable function (default)

But it may not be a problem at all.

Bilu

Does anybody know if these work?

v4mv
Allow 4 motion vectors per macroblock (slightly better quality). (default: disabled)
(is this MPEG-2 compliant?)

autoaspect
Same as the aspect option, but automatically computes aspect, taking into account all the adjust- ments (crop/expand/scale/etc.) made in the filter chain.


Bilu

bilu,

Yes, what you proposed is like a hi-quality CBR, but note, this is not what we want (or at least me). Because you still can't lower the average quality, you see? I want mencoder to keep constant quantisizer, except when this will result in bitrate higher than specified. If this constant quantisizer could be specified in fractional way, that would be solved, but minimmum quantisizer can only have integer values (it seems)...

v4mv, if I remember correctly, crashes if used with MPEG2 in mencoder.

Quantizer=2 -> Maximum quality
Average=Maximum -> Pull the bitrate to the maximum (quantizer to the minimum -> q=2 unless bitrate > maxrate)

In this specific case (q=2) I can't understand the difference. Can you explain a bit more?

Bilu