2nd pass file undersize. How can I increase quality?

[SpeakerBR]

Hi,

I am enconding a video, but the file is 18MB shorter that I prefer. my settings are at:

http://forum.doom9.org/showthread.php?p=913622#post913622

The video is enconding with all frame to the minimum quantizer: I-frames and P-frames at 2 and B-frames at 4.

What is the better for increase quality:?
-Set Min B-frame quatizer at 1 (Before I set it at 2). OR
-Set Max consecutive BVOPs at 1 (Before I set it at 2).

Thanks very much. Sorry for my poor english.

[Sharro]

:search: :readfaq: :readrule:

There's a sticky called oversized/undersized explanations........

All the best,

Sharro

[foxyshadis]

Neither. Use a matrix that retains more detail, or downsize less.

There's a thread in this forum called Xvid Presets (http://forum.doom9.org/showthread.php?t=119399) that will give you step-by-step directions on how to make higher quality video instead of just filling up space.

[Blizzardstar]

I understood how it works, but not quite how to use it, do I need to know how to use Avisynth?

[foxyshadis]

Not really, but knowing how gives you more flexibility to adapt your movie to your requirements, as well as fixing any issues that might be inherent in it. All you really need is to use the Enc tool.

[HeadBangeR77]

The video is enconding with all frame to the minimum quantizer: I-frames and P-frames at 2 and B-frames at 4.
Apart from what has been already said, it's not a good idea imo to set the min. quantizer for b-frames at 4. B-frames would get lower quantizer's values without it, because they are calculated by multiplying by ratio and adding the offset.
If you set the minimum to 4, you're gonna get higher B-frames' quants and thus bigger jumps in quality, which is not a good thing quality-wise. Imo the minimum for all frames should be set evenly.

[unskinnyboy]

If the codec is maxing out on your current settings, maybe you don't need b-frames at all. So try with b-frames turned off. Also turn off AQ. You are not starving for compressibility here that you need AQ. Doing a comp. test before the actual encode will tell you where you stand regarding compressibility.

[foxyshadis]

A 2-pass undersize with V3HR sounds like reducing the resolution way too much, though - especially if the screenshot posted in the other thread is any indication (384x224).

[SpeakerBR]

I response to myself. The better is Set Min B-frame quatizer at 1

I enconding using the two options. Both are well, but the second option make PFrames with Q=3:

http://img54.imageshack.us/img54/5760/4doom9sm1.jpg

The first option make all IFrames with Q=2, Pframes with Q=2 and VBops with Q=3-4.
The second option make all IFrames with Q=2, but Pframes with Q=2-3 and VBops with Q=4-5.

There's a sticky called oversized/undersized explanations.

It's an advances subject. The FAQ don't talk about this.

Use a matrix that retains more detail, or downsize less.

I use the matrix EQM V3HR. It is good for me. Another matrix can cause compatiblity problems.

So try with b-frames turned off.

Now I got ALL Iframes and Pframes with Q=2. If I limited BFrames, I got Pframes with Q=3.

especially if the screenshot posted in the other thread is any indication (384x224)

Sorry, I forgot tell that the resolution is 716x404.

[unskinnyboy]

I'm having a tough time understanding you.

Now I got ALL Iframes and Pframes with Q=2. If I limited BFrames, I got Pframes with Q=3. So what's wrong there? Lower the quant, better the picture.

So, did your undersizing go away or not?

[jon.schaffer]

The better is Set Min B-frame quatizer at 1
The best thing is to set it to 2. When you set it to 1, it's useless since the formula that is used to create B-frames only allow to create higher quantizer B-frames, i.e. Q3.

But, if you set it to 1, when min I-frame Q=2, the result is the same... OK, it was a purely rethorical answer.

Now, onto the subject: you said that THIS encoding is undersized, right? So, how can it have Q4 and Q5 frames?
An typical undersized file is when the codec only creates Q2 (I/P) and Q3 (B) frames...


[Edit: should have write: A typical undersized file is when the codec only creates Q2 (I/P) and Q4 (B) frames (or Q3, depends on your B-frames settings)]...

[SpeakerBR]

I'm having a tough time understanding you.

Sorry, english isn´t my native language.

So what's wrong there?

The wrong is that before the video hasn´t PFrames with Q=3. If I limited BFrames (the second option), I got Pframes with Q=3 and the quality lower.

Now, onto the subject: you said that THIS encoding is undersized, right? So, how can it have Q4 and Q5 frames?
An typical undersized file is when the codec only creates Q2 (I/P) and Q3 (B) frames...

This image is the video if I Set Max consecutive BVOPs at 1. The undersize video has ALL IFrame & PFrame Q=2 and ALL BFrame with Q= 4.

For obtain a 700MB video, I set Min B-frame quatizer at 1. So the 700MB video has ALL IFrame & PFrame with Q=2 and VFrames with Q=3-4.

[unskinnyboy]

Two questions...

1) What exactly do you mean by "limiting" b-frames here?

2) I once again ask, did your undersizing go away or not? Means are you still getting undersizing?

[jon.schaffer]

The undersize video has ALL IFrame & PFrame Q=2 and ALL BFrame with Q= 4.
That is the expected result.

For obtain a 700MB video, I set Min B-frame quatizer at 1. So the 700MB video has ALL IFrame & PFrame with Q=2 and VFrames with Q=3-4.
Once again, this is useless. You set min B-frame quantizer to 1, but the codec does NOT create such Q1 B-frames... If you set it to 2, you'll get the same result (even if you set it to 3...).
What bothers you with this last encoding?


I got a doubt here: what B-frame formula can create Q3 and Q4 B-frames with only Q2 I/P frames?

[HeadBangeR77]

I got a doubt here: what B-frame formula can create Q3 and Q4 B-frames with only Q2 I/P frames?
The default one i.e. ratio=1.50 and offset=1.00, since it gives Q3.5, and probably is rounded either to Q3 or Q4 (depending on codec's mood ;)).

[Didée]

Nope, default settings won't give that, since

2 * 1.5 + 1.00 = 4.0

so with default settings Bframes basically won't ever go lower than q4. (Except for adjustments due to underflow, eventually.)

Try: Bframes: max = 2 or 1 / mul = 1.6 / offset = 0.00

[HeadBangeR77]

Nope, default settings won't give that, since

2 * 1.5 + 1.00 = 4.0

so with default settings Bframes basically won't ever go lower than q4. (Except for adjustments due to underflow, eventually.)

Try: Bframes: max = 2 or 1 / mul = 1.6 / offset = 0.00
Gosh, I must have yet another coffe, since I can't multiply on the level of primary school. :o