Emulating CBR with VBR...

[Chainmax]

A few of my recent encodes have been done at 8000kbps. Since CCE's one pass CBR is so innacurate, nasty bitrate spikes are quite usual and the standalones I tried them on stutter at those spots. Therefore, I though about using one of two alternatives for more accurate CBR:

- Multipass VBR; 1 pass; min=7900,avg=8000,max=8100
- One Pass VBR; Q=?; min=7900,max=8100

Which one of these two would be preferable and how does each compare to One Pass CBR speedwise?

[Trixter]

Neither -- honestly, your best bet is CBR. That's because CCE essentially treats VBR and CBR as exactly the same, but with different parameters: CBR is VBR but with identical values for all three parameters (min, avg, max). Have you tried 2-pass CBR?

I too have been suffering from bitrate spikes; I told CCE I didn't want to go above 8000 but using bitrate viewer found 2 or 3 spikes above 8500. It's only for one GOP but it's annoying. For those sections, I use SP's "VBR Bit Allocation" feature to isloate where the spikes occur and lower the maximum to 7000 so that, even if it spikes, it's under what I need.

Irritating, yes, but it's worth the hassle because, for me, CCE's output quality is the best of any encoder I've used.

[Chainmax]

Using 7000kbps average is an extremely inefficient solution, as even at 8000kbps my videos don't take up all the disc. How come CinemaCraft never bothered to include a proper CBR mode?

[Trixter]

Using 7000kbps average is an extremely inefficient solution, as even at 8000kbps my videos don't take up all the disc. How come CinemaCraft never bothered to include a proper CBR mode?

They did; some people have no problems with it at all. I just encoded a 10-minute diverse clip at CBR 8000 and bitrate viewer shows that it did indeed stick to it.

It's only on very longform projects that things can go off. The project with a single spike over the bitrate that I'm working on right now is over 3 hours long...

[mp3dom]

Have you tried the CBR Multipass feature with "Equalize each GOP bit's length" option enabled?

[Chainmax]

"Multipass CBR" is an oxymoron. I might as well just use 3-pass VBR instead. Would "Equalize each GOP bit's length" give more stable single-pass CBR results? How would overall quality be affected by it?

[mp3dom]

The Multipass CBR is useful to obtain a more stabler and constant bit allocation for GOP. Also the bit allocation for each picture in a GOP is modified at every pass to obtain the best results.

The "Equalize each GOP Bit's length" is an option that force the amount of bitrate per GOP to be equal. This option is designed for CBR (in CBR a slight bitrate movement is allowed to improve the image quality but if your target bitrate is near to the maximum allowed by DVD specs the bitrate movement could lead to a buffer overflow.)

I have made a 1 hour DVD with a 5-pass CBR at 9250 Kbps + 2x 224 Kbps Audio (448 total) + 4 subtitle stream (it's a 16:9 presentation) and compiled with Scenarist without any problem. No buffer overflow or blocks or stutters at all.

[Trixter]

"Multipass CBR" is an oxymoron. I might as well just use 3-pass VBR instead. Would "Equalize each GOP bit's length" give more stable single-pass CBR results? How would overall quality be affected by it?

I know that "multi-pass CBR" seems like an oxymoron at first, but it's not: CBR ensures constant bitrate, but multiple passes give CCE a chance to squeeze extra quality out of the same bitrate.

Equalizing each GOP's bit length is used mainly for multi-angle titles which have very strict playback requirements. Quality is affected somewhat, but I'm willing to bet that any bitrate spikes you may be getting now will completely disappear if you enable it.

[Chainmax]

I see, but why not just using plain 3-pass VBR then? Wouldn't that take the same amount of time and have higher quality?

[mp3dom]

Multipass VBR sometimes allow bitrate spikes that could lead to buffer overflow (tested with multiangle but not with standard video). The "Equalize etc etc." delete the spikes but works for CBR, hence the option for multipass CBR.
I think it's better the Multipass CBR at (i.e.) 9000 Kbps + Equalize GOP than a multipass VBR with a max bitrate of 8800 Kbps

[Chainmax]

So I can't have CBR and speed and am pretty much screwed then :(.

[Trixter]

So I can't have CBR and speed and am pretty much screwed then :(.

Well, you could go to 2 passes instead of 3. It would still be better than 1-pass...