FORUMS: list search recent posts

Constrained VBR & Unconstrained VBR

COW Forums : Compression Techniques

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
Stephane Bastien
Constrained VBR & Unconstrained VBR
on Dec 15, 2005 at 7:19:31 pm

Where can I find some good information about the differences between Constrained VBR & Unconstrained VBR for WMV encoding? I have Ben's book, but I don't see any mention.

Thanks

St


Return to posts index

Craig Seeman
Re: Constrained VBR & Unconstrained VBR
on Dec 16, 2005 at 3:43:51 am

Basically Constrained sets an upper limit to the variable bit rate. In certain parts of a VBR encode, a very complex frame by frame change can create a very high bit rate peak. Constrained prevents that from happening by setting an upper limit.


Return to posts index

Charles Simonson
Re: Constrained VBR & Unconstrained VBR
on Dec 20, 2005 at 11:46:54 pm

Also, with most Windows Media encoders, the peak bit rate of a constrained VBR encode refers to the max average a bit rate can achieve over the specified buffer time zone. So, if your peak is set to 18Mbps, and the buffer is set to 5 seconds, then for that 5 seconds, the peak is allowed to go over 18Mb, to even say 22Mb if necessary, as long as the average for any five seconds including that 22Mb frames aren't over 18Mbps total. If the encoder you are using uses this method, and you need tight control over the max bit rate that can be applied, you need to either set the buffer time lower or the peak bit rate lower and closer to the average bit rate than you normally would with other codecs.



Return to posts index


Ben Waggoner
Re: Constrained VBR & Unconstrained VBR
on Dec 31, 2005 at 9:34:11 pm

I'm sure I covered this in there somewhere...

Anyway, I recommend you stay away from non-peak constrained VBR. There's pretty much always a maximum peak you'd want to use in a particular application, even if it is crazy high. There's no downside to specifying a peak.


Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2017 CreativeCOW.net All Rights Reserved
[TOP]