benefits of constant bit rate versus variable?

[Daniel_l]

Variable bit rate (VBR) encoding will generally give you higher quality for a smaller final file size. Usually takes much longer to encode than CBR as generall VBR requires 2 passes for the encode and CBR usually does this in one pass (although some tools allow 2 pass CBR)

[Accountneedsrealnameupdate]

If you only have a 10 – 15 min programme how does 2 pass make it better?
It will make it smaller, yes, but better??

[Daniel_l]

You could say that a VBR encode with an average bitrate of 4Mbps and a peak of 8mbps will be equal in quality to a CBR encode of 8mbps. However the VBR file will be more efficient.
You could also say that if you did a VBR encode with an average bitrate of 2mbps and a peak of 4mbps that it will be of higher quality than a CBR encode at 3.9mbps.

Both VBR encodes will usually result in smaller file size.

CBR has the potential to waste bits
VBR makes a better use of bits

Apart from the datarate the only things that make it ‘better’ are the source and the encoding application and CODEC.

[Jeff Nelson]

This would seem to me to say that it’s nearly always better to use VBR (unless you’re in a hurry to encode or have a project where space isn’t an issue).

I use Cleaner XL to encode stuff to mpeg 2. I know there’s a range of encoding software and hardware out there. What kind do most people here use, just out of curiosity?

[Chris Borjis]

Tsunami is my encoder of choice.

Cinemacraft is also excellent.
A little faster too.

Procoder is arguably the best one of all.

All of them offer 1-Pass VBR btw.
It’s quite common now and thats how the set top DVD recorders
achieve flexible recording mode, with realtime VBR.

[Eric Pautsch]

I would say ALWAYS use CBR unless space is an issues. Low cost encoders tend to deliver bitrate spikes once and awhile that send your overall bitrate over the 9.8 limit.

[Accountneedsrealnameupdate]

VBR – Smaller file size yes
But is the picture quality any better.
A 10 min programme cbr at say a data rate of 7, and a vbr at any settings, will the vbr be a better picture.
For these small programmes size/efficiency is not an issue, just best pic quality

[Dave Friend]

[daniel_l] “You could say that a VBR encode with an average bitrate of 4Mbps and a peak of 8mbps will be equal in quality to a CBR encode of 8mbps.”

I think that if you test this theory you will find that the CBR looks better.

[daniel_l] “the VBR file will be more efficient.”

True, read any description of VBR encoding and it will say VBR is more efficient. However, it is important to understand what efficient means in this context. It means the use of fewer bits of data to reproduce an image. In other words, the image is more highly compressed. Efficiency is demonstrated by requiring less input for the same output. The term has no additional meaning in this context.

It is possible, depending on the image contents, a higher compression would not be noticeable, but it will not ever look better.

[daniel_l] “You could also say that if you did a VBR encode with an average bitrate of 2mbps and a peak of 4mbps that it will be of higher quality than a CBR encode at 3.9mbps.”

You could say that, but it would not prove to be a correct statement. Try it using your favorite encoder and you will see.

[daniel_l] “Both VBR encodes will usually result in smaller file size.”

True, which points directly to the reason for VBR encoding: Cramming more program length into the same number of bits. There is no other reason to use VBR. If the program will fit in the available space (e.g. on a DVD) at a given CBR encode, then there is usually no reason to employ VBR encoding.

Dave

[Jeff Nelson]

Downloaded this program to try it out, put 4 1-hour segments into it to do. It did them, except it did them all as one big 4-hour mpeg, rather than 4 separate 1-hour mpegs. What did I do wrong? How can I put multiple segments into it and have them come out separate segments rather than together as one long one? Thanks.

[Accountneedsrealnameupdate]

At long last somebody else agrees, that if space is not an issue, cbr is probably better than vbr.
All frames getting the same compression, not some 3 some 5 some 7.
Plus half the compression time.
Thanks Dave