Nandub: Crosspoint ???

[JamesTKirby]

Hello,

I've used Nandub a lot, and always set the crosspoint at 270 for 1CD and 450 for 2CD encodings.

I'd finally like to know how to set it properly! I've looked around in several FAQs and in the Nandub readme but haven't really grasped how it works.

Should I just play with the crosspoint value and keep re-hitting the "calc" button until it has the slowest compression percentage?

Any help would be appreciated.

Thanks in advance,

JTK

[iago]

@JamesTKirby

Yes, first set a reasonable crosspoint value (230-280 for 1CD / 350-460 for 2CD as Doom9 points out in his guide) then hit the calc. button. Until you reach the curve compression ratio you desire, try tweaking the crosspoint value within the above mentioned ranges.

good luck ;),
iago

[JamesTKirby]

Originally posted by iago
@JamesTKirby

Yes, first set a reasonable crosspoint value (230-280 for 1CD / 350-460 for 2CD as Doom9 points out in his guide) then hit the calc. button. Until you reach the curve compression ratio you desire, try tweaking the crosspoint value within the above mentioned ranges.

good luck ;),
iago

Well thanks iago, but that doesn't really answer my question.

I'd like to know if the goal is to get the lowest possible compression ratio ? I know this is might sound like a dumb question - of course we "desire" a low compression ratio but is that really what we are after ? I mean does a too low (good) a compression ratio produce the best results overall... or do we get really nice looking movie with 5% of the frames looking really bad...? Of course it depends on the movie content.

So:

Is the lowest possible compression ratio the ultimate goal to shoot for ?

Sorry if this a silly question but I'd really like to know ;-)

Thanks,

JTK

[iago]

Originally posted by JamesTKirby
Is the lowest possible compression ratio the ultimate goal to shoot for ? Well, it's not the "ultimate" goal imho, but only "one of" the goals we aim to reach at. It's only one of the many parameters (ok, of course an important one) that affect the results of your encode. (Some people even prefer to leave it at "0" :)).

Regarding the best possible encode (and the parameters to be used together with the selected bitrate and aimed video size), what I can only say is that it depends on the movie itself: in other words the compressibility of the movie, which you can calculate using the first pass stats file, loading in GKnot and checking the value it spits out. A number higher than 60 mostly ensures the quality of your encode and it's not a good idea to go lower than 40. Another method is to load the stats file in NandubStatsReader and record the size(MB) value, then divide it by your aimed video size (in MB). To be on the safe side, firstpass/secondpass ratio should not be higher than 2.5.

I don't know if this will be helpful for you, but I don't know any other secret method actually ;). First and foremost: compressibility check. Then tweaking the parameters accordingly...

best wishes,
iago

[JamesTKirby]

Well, that pretty much clears things up for me.

Thanks, iago =)

Happy encoding to you!

JTK

[sid]

How do i have to tweak the settings accordingly to the parameters gknot or nandubstatsreader spits out ?

[manono]

Hi-

The easiest and fastest way is to do the Compress Test. Then just adjust the resolution up or down based on the percentage value. Or, if the value is too low, consider using an extra CD.

[MadScientist]

helloo i thort i'd revive this thread and ask why there is a crosspoint variable in nanbub. i cant program in c++ so the source code is not much use to me for solving that problem. can i ask what the crosspoint does (not how to set it:p) and if anyone is a nanbub wizz the part of source code that the crosspoint is "programed in". thanks ^_^ :)

-MadScientist

[esby]

Iago,

Yes, first set a reasonable crosspoint value (230-280 for 1CD / 350-460 for 2CD as Doom9 points out in his guide) then hit the calc. button. Until you reach the curve compression ratio you desire, try tweaking the crosspoint value within the above mentioned ranges.


Are you implying (or suggesting, that don't matter)
that calculating optimal crosspoint should be done before any second pass?
In this case, the cross point choice value should be a nandub sbc setting,
in term of ergonomy, not an obscure setting lost in the old vdub option...
Am i wrong?

esby

[MadScientist]

lol i knew some one would say "230-280 for 1CD / 350-460 for 2CD"
Ok maybe i wasent clear. what does the cross point do?. i have read the readme file and still dont understand. why was it implememted?. I know i cant set it to zero and set the compresion modulation manualy?
please dont post "230-280 for 1CD / 350-460 for 2CD" again thats not what i'm asking for:(

Are you implying (or suggesting, that don't matter) that calculating optimal crosspoint should be done before any second pass?well that would be hard for me to do since i dont know what the hell the cross point is :D

i know y=x is a simple copy of the stats file and y = Ax is the linear based modulation set by the user where ; 0 < A < 1 .

K = the modulation that the cross point predicts(when u press the calc button), but what are the other 2 points C & that gray blob thing, what are the scales, i assume very few people will understand this