D4/5 using an extremely high bitrate to encode the ending section of a movie

[yingx2]

Hi, I posted the following question in the D4 encoding section, and then I realized that now it's practically like a dead forum.:(
(or my question was too stupid, I don't know.)

Anyway, here's the question:

Does anyone ever notice that DivX4/5 tends to use a higher bitrate to compress the ending part of a movie when adopting 2-pass mode?

For example, if you cut your compresssed, 120 min movie of 700MB into 2 parts--the first 115 min part and the last 5 min part--you might end up with two files with two totally different bitrates. The first part could only amounts to 600MB while the last 5 minute part stoled the rest 100MB from you.

I've done some experiments on this and got similar results. It doesn't matter whether your last part is like ending credits or a low/fast motion secene, the last 5-10 minute clip must be really really big!

It appears that divX has a natural tendency to encode the final section of a film with an extremely high bitrate so that the final, average bitrate can be close to the bitrate we enter in the codec setting menu.

Any ideas?

Another question:

I always keep the original resolution of my source(usually 720x480), but I remove black borders without cropping the picture. Is this called shrinking? Which resize filter should I use if I prefer sharp images?

any suggestions will be appreciated.

[HateBreeder]

And so did many other people.

It was there since divx 3!

that's why encoding packs like Gordian Knot, offer the
ability to "trim" the movie into to parts, the actual movie,
and the end-credits.
It automatically offers to encode the ending credits with
low bitrate while encoding the movie part at High
bitrate VBR mode.

Thus, increasing output quality for the movie.
("gives it more bitrate")

Regards.

[yingx2]

That's news to me.
In fact, I am new to this scene (for about 3 weeks) .
Anyway, it's good know that I'm not the only one having this problem.
Thank you very much.
I'm gonna try gordian knot later.:)

Still, which resize filter should I use given the above setting?
(or I don't have to use any? )

[sibe]

I remove black borders without cropping

How do you do that? As far as I know: removing black borders=cropping.

[yingx2]

I do remove black bars.
But I don't crop the image itself--the main part that has no black areas in it.
Some people remove black borders, as well as a small portion of the edge of the main picture, but I prefer not to crop the picture itself.

I believe you did auto-crop before.:)

Is my English that bad?

[athos]

In VirtualDub, you would use the null filter and then crop. the null filter is there if you want to do nothing else than crop.

Even though your are not removing part of the actual movie, you are still cropping because technically the black bars are also parts of the picture. You should consider cropping away maybe one pixel of the actual movie picture, because the solid black parts do not use up a lot of bits when encoding, but the threshold between picture and black does.

[DJ Bobo]

I was also surprised that the credits take so much bitrate (I thought it is exactly the opposite!)

That's why I encode the credits separately always quality based 0% or 0kbps. Even then they take about 700kbps :angry:
But that will save about 40MB that can be used to make the movie look better

[Acaila]

To prevent the codec from using too much bits on the credits you should encode them with fixed quantizers. This way it has no choice but to encode as you tell it to. XviD has some nice options for this without needing a seperate encoding for the credits, but for DivX4/5 you do need a seperate encoding.
I always use fixed quantizers of 31, and that works nicely, they never come out too big.

[yingx2]

Even if the credits only took 15 or 20MB, I still think it's too big for my 1-CD rip. That's why I usually choose to remove them, but that makes the whole movie sort of "incomplete" and end very abruptly especially when the ending music plays before the the credits start to fall.

I'm working out a way to keep the first 10 or 15 seconds of the credits and let both the picture and the music fade out smoothly. After all, they are really not so important.

Don't know how to do it yet:(

[athos]

It doesn't matter whether your last part is like ending credits or a low/fast motion secene, the last 5-10 minute clip must be really really big!
How will encoding the credits with a fixed quantizer solve this?

[Acaila]

Because if you tell it to stick to a certain bitrate it will still fluctuate around that bitrate, but if you tell it to encode with fixed quantizers it will use only those quantizers and thus not have the ability to use a high bitrate.

[athos]

Yes I understand that. However this requires that the credits are not allready cut out. I think yingx2 meant that DivX movies tend to use a higher bitrate at the end of an encode, no matter if there are credits or even high motion material. You probably dont want to encode the ending of the actual movies with fixed 31x quantizer.

[dragoman]

Hi,

That's why you have to create seperate avs files for the movie and the credits, like Gknot does automatically for you.

Easy to do this in Dvd2avi, just use the "[" and "]" buttons...

dragoman

[Acaila]

But then you'd still have the problem of the end of the movie being encoded with higher bitrate, correct? I can't remember ever having seen that behavior myself, but then I haven't looked for it either.

I know XviD doesn't do this as I have monitored it's quantizers during encoding, and they all look normal.

[dragoman]

@acaila

No, not if you encode them serperately.

My method (right now I'm using DivX 5.0 Pro, so no Gknot for me :(

is to seperate the main movie and the credits (ending and beginning, depending on movie) in dvd2avi, creating different avs files for them in Gknot.

Then I just encode the beginning/ending credits at 1-pass quant=31, and the main movie in regular 2pass mode.

Load it all into job control in Vdub and let it run....then you just gotta mux the video and the audio.

dragoman

(edit) Ooops! Sorry, didn't see the point until now...Well, I think this is only a problem when using a program like Gknot that forces the codec to use a certain filesize. The program adds all those extra bits to get the file bigger.

DivX 5.0 Pro has no way to set a final filesize, so as far as I can tell this problem doesn't exist.

Could it be only this problem exists when using Gknot? If you use Vdub to encode a divx4 movie does it do this?

dragoman (2nd time)

[Acaila]

GKnot is just a program that chains other programs together. It doesn't affect the codec directly, it just tells VDub what bitrate to use. Which means that if you don't use GKnot you could see the same thing.

Can anyone confirm that?

[dragoman]

Hi,

Before DivX 5.0 Pro came out, I only used Nandub with Gknot, so I can't say that Vdub did this with DivX 4.xx

I can say that this is not happening with DivX 5.0 Pro using Vdub 1.4.7.

dragoman