Understanding variable bit rates (1 Viewer)

[John_Berger]

This is more of a technical curiosity than anything else, but every web site that I visit gives me a definition for "variable bit rate". Well, DUH! Could it possibly mean that "variable" means "changing"? Imagine that. :rolleyes

I'm starting to play with variable bit rates now that (from what I understand) DVDit PE has better chapter support for variable bit rate MPEG-2 files, so I'd like to take advantage of that. But I'm just curious about it because I still need to set a bit rate when creating the MPEG-2 file.

What's the purpose of this setting? Maximum bit rate? Average? Optimal? How does the encoder determine the best per-frame bit rate based on this number?

Again, just technical curiosity, but most web sites that I've seen give me the vanilla definition that I already know.

 

[Ken Chan]

http://tangentsoft.net/video/mpeg/enc-modes.html

http://www.tecoltd.com/enctest/concepts.htm

http://dvd-hq.info/Compression.html (TMPGEnc)

http://www.research.ibm.com/journal/...westerink.html (technical)

//Ken

 

[John_Berger]

Thanks! I figured that it was more of an average than anything else, but I wasn't sure. Unfortunately, MSP 6.5 appears to be 1-pass VBR. Maybe that's different in v7.0.

As to that last link ... you intentionally wanted to see if my brain would explode, didn't you?

 

[Ken Chan]

Didn't work, huh?

If an encoder did two-pass VBR, it would probably mention it prominently, since it is a higher-end feature.

//Ken

 

[John_Berger]

Didn't work, huh?

Nope. :p) I wouldn't give anyone here the satisfaction of letting it work.

Oh, well. I think that I've become a VBR convert, though. I kept bumping up the VBR rate to be much higher than a CBR file would have been able to put onto a DVD and it still ended up being a smaller file than the DVD could hold. So, I bumped up the bit rate and re-encoded again.

Actually, the DVD (on DVD-RW) is finished downstairs. Time to see how it turned out. My first VBR DVD. { crossing fingers }

 

[John_Berger]

ime to see how it turned out. My first VBR DVD.

Oh ... my ... God.

I am definitely a VBR convert! The quality of the DVD is absolutely GORGEOUS! I would have had to reduce the CBR rate by several hundred Kbit to fit this on the DVD. I saw absolutely no pixelization either.

{CARTMAN} Swee-ee-ee-eet. {/CARTMAN}