VBR versus CBR? Is it really different?

[nkuperw]

Hi, I have a bunch of avi's that i'm trying to put back into DVD's and i'm wondering whetehr or not to go 2-pass (or n-pass) VBR or single pass CBR? Is the quality that different? Considering that i'm starting from an avi (either divx or whatever) and the quality is somewhat shot anyways, will I get a substantial diffenece in the final outcome when I change the encoding settings?

thanks

[SLK001]

If you don't bitrate starve your encoder, then a VBR can be as good as a CBR encode. However, it usually takes 2-4 passes to properly allocate the bitrates for VBR.

[nkuperw]

I guess from what you're saying is that a CBR will generally give you better quality than VBR if you're not limited by space, but if limited, a VBR will be better? For eg, if I do a CBR at say 6000, will I get a better image than if I do a 2-pass VBR at 4000?

[SLK001]

If the encoding parameters are set properly, then CBR and VBR differences will more likely not be distinguishable. For instance, a VBR with a MAX BR of 6Mbps could look as good as a CBR at 6Mbps, but the size advantage could be huge.

But, if you're not limited by space, then use a CBR.

[bugster]

With VBR, the main figure to concern you should be the Average. Sure Max and Min play a part, but the Avg is the most important one.

A CBR encode at 6Mbps will be the same size as a VBR encode with an Avg of 6Mbps. However, dpeneding on the source material, and the fact that the VBR encode will have a higher MAX bitrate, high motion scenes are likley to look better on the VBR encode.

6Mbps is actuall a pretty high bitrate so CBR Vs VBR at this level will show little difference. VBR really comes into its own with longer material. If the length of your movie requires say 4Mbps to fit on one DVD, then VBR will be a big improvement over CBR, assuming the source material is not flashing lights and fast movement from one end to the other!

Have I made sense?

[ZippyP.]

VBR allows you to squeeze more minutes per disk while maintaining quality. If that is not an issue, then just use CBR with a high bitrate.

[nkuperw]

Yes, it makes perfect sense. But now, if I may add another layer to this onion....if the source material is not excellent, but not bad either, for eg. a divx rip of a DVD (and even that has a fair amount of variability), what would be better? I understand that a VBR would give a better result than a CBR at an equivalent setting (say 4MBP), but I guess what I'm asking: how much better would the "garbage" out be and it would it be worth the time it takes to do multi passing?
I think I may know the answer, but I'm hoping to get some feedback from the "cogiscenti" in this field.

Thanks

NK

[next]

My opinion here is that the argument was more credible in the "jam as much video as you can on a CDR" days. Ergo - time versus quality encoding with limited CDR real estate was a science.

With DVD-+R and DVD authoring moving to the masses I feel the difference in quality is minimal. If encoding time is a factor then CBR will not be as much of a quality issue when compared to VBR encodes.


Probably not even an issue unless we are talking some really long encodes.

[mh2360]

I do a lot of Divx-DVD conversions. Divx is a good format, but most files you find around the net, if played on a stand-alone Divx player, on your regular TV, would not be DVD quality, they just look good on a small PC monitor. Trying to squeeze every bps on to a DVDR is a waste of time in my opinion. You are never going to get full DVD quality from a regualr 2 x 700mb Divx movie. CBR is fine for bitrates above 4500, anything below I will use VBR, but even then never more than 2 passes.

[next]

I do a lot of Divx-DVD conversions. Divx is good format, but most files you find around the net, if played on a stand-alone Divx player, on your regular TV, would not be DVD quality, they just look good on a small PC monitor. Trying to squeeze every bps on to a DVDR is a waste of time in my opinion. You are never going to get full DVD quality from a regualr 2 x 700mb Divx movie. CBR is fine for bitrates above 4500, anything below I will use VBR, but even then never more than 2 passes.

Great perspective. I'm not a real divx fan because of the points you raised. But for mobility and PC notebook or desk top playback it's great. A huge cpu performance issue but look at the power we get now for small dollars. A super format and always improving - it could dominate. Especially with broadband and the sharing issue.

My cut off is very similiar to yours - around 4500 for cbr on dvd.

[SatStorm]

VBR shines on long caps. On short ones (less than 10 min) it actually might harm the quality if the difference between min/aver/max is big....

For example, cap a 4 Hour VHS, filter it, and encode it @ 352 x 576 with 800 min, 2300 average, 3800 maximum bitrate. This way 4 hours are on a DvD-R disc and the picture is perfect.

Now cap the same tape to 10 min clips seperate , and using the same settings encode. The picture suffers... Use close to average values in this example, and the result is much better. Or use CBR and get easy perfect results!
This is my opinion of course. Others on this matter may have another!

[Limulus]

when working with main concept (vegas video) encoder only allows 1-pass VBR, i have my doubts that is better than CBR when filesize aint a problem and you are on higher bitrates around 9000. anyone knows more about ?

[mh2360]

I decided to do a little test. Below are two identical 20 second clips (video only) of a fast moving action scene converted from Divx. One is encoded at 8000mbps the other at 4000mbps using Tmpgenc with the highest quality settings.

http://www.mh2360.pwp.blueyonder.co.uk/clip_8000mbps.mpv
http://www.mh2360.pwp.blueyonder.co.uk/clip_4000mbps.mpv

Although the difference in bitrate is huge, the quality is almost the same.