Advantages of Variable Bitrate over Constant Bitrate?

[Beev]

What are the main advantages of encoding with a Variable Bitrate over a Constant Bitrate? Also, what is the advantage of encoding with a 2-Pass VBR?

I know that the VBR outputs higher quality, but is the quality so drastic that it should be used? I think (from what im told) the 2-Pass VBR just analyses the file first. What is the point of this?

Thanks in advance.

[teegee420]

The whole point of 2-pass VBR is more efficient allocation of the available bitrate. It should really only be used for low bitrates when you're trying to squeeze video that is longer than what is considred "safe" for good quality. For instance, some people don't like to put more than 90 minutes of video on a DVD. If it was necessary to put say 110 minutes, that would be a good situation to use VBR. Single pass VBR pretty much accomplishes the same thing, but final file sizes aren't as easily predicted as doing two passes. If conserving disc space isn't an issue you should probably just run a CBR encode.

[flaninacupboard]

I'll wildly assume you're talking about VCD.
a 700meg CD-r will hold 6512640 kilobits of data. you could set that for one second of video (at 6512640kbps) or 100 seconds (at 65126kbps) or a more realistic figue, 3600 seconds (at 1809kbps). Now say 30 minutes of your video are two people sat in a room talking. this scene needs say 900kbps to look good. if we were encoding at 1809kbps we're wasting 900kbps a second. now say your other 30 minutes is explosions and car chases needing 2700kbps to look good. if encoding at 1809kbps we're starving our video of 900kbps.

The logical solution is to encode with VBR. this way our low action 30 mins is encoded at 900kbps and our high action at 2700kbps, giving us much better quality in a file the same size as CBR.

obviously this is a gross oversimplification, but the theory behind it is corret.

[mats.hogberg]

...but then again, there's no such thing as a VBR VCD...

/Mats

[flaninacupboard]

smartarse

I'll assume you're talking about an (X)(S)(C)V[C]D

[mats.hogberg]

/Mats