CBR vs. VBR

[Michael Sage]

I need some suggestions: I'm rendering a couple of projects to MPEG2 from Vegas5b for use in DVD Arch 2a. I have completed one project, and used a CBR of 8,000,000. I used 8,000,000 because I saw somewhere that any higher may not be compatible with all DVD players.... I was under the impression that a high CBR would produce the best quality over a VBR ( I think I may be wrong on this )

I don't care about rendering time... I want the best quality DVD that I can get with the MainConcept encoder.

I'm shooting 24p advanced, and would like to know if CBR is better than VBR. I see where I can select a 2pass VBR, but not sure what VBR settings to use ( if indeed this method produces a better quality ) Any suggestions?

[Jan Crittenden Livingston]

<<<-- Originally posted by Michael Sage :

I'm shooting 24p advanced, and would like to know if CBR is better than VBR. I see where I can select a 2pass VBR, but not sure what VBR settings to use ( if indeed this method produces a better quality ) Any suggestions? -->>>

The highest quality DVDs are done with a VBR, 3 pass. So I would imagine that while it would take longer the 2 pass VBR would be better that the Const Bit Rate.

Just an idea,

Jan

[Rob Lohman]

A good encoder should give better results with VBR. As Jan
indicated almost all professional discs use VBR encoding.

[Rob Easler]

I think it depends on what kind of stuff you are compressing. On my wedding video montages where I use certain effects like white flashes and text or any text on black I get better results with CBR. With the VBR and some of my effects, especially noticable with white flashes or white fades and text the bit rate goes lower during those sectins because there is not as much info to compress and so those parts can get grainy using VBR. With the bitrate os always the same high rate so I don't get the grain.

I know VBR is a way to save space because on slower moving scenes the bitrate drops and I know it could provide better compression decisions because of the two pass but the name itself "variable bitrate" to me seems to indicate fluxuations in the bitrate and that alone wouldnt seem to me to mean higher quality all the time. Anyway, I am no expert but I am sure I get better results, at least on the stuff I mentioned above with CBR and I have not been able to discern higher quality on the other stuff using VBR as long as I use the 8,000,000 CBR.

[Rob Lohman]

One the main reasons why VBR usually is better than CBR (besides
allowing for a lengthier film in the same space) is that it is multiple
pass encoding. So it will at least go 2 times over your footage but
usually 3 times etc. This will allow it to much better analyze the
footage and allocate bits where they are really needed. It can
evaluate the compression it has done in a previous stage to
futher finetune it. Again this is highly dependend on the encoder
you are using!!

Ofcourse there might be cases where CBR will do a better job,
I can imagine a high bitrate CBR with plenty of room might do
a better job (as you indicated with certain shots). However, a
good quality encoder should in theory get at least the same
quality in VBR and usually better.

If you get a chance try a demo of Canopus ProCoder 2 (or
Express), see what that does with the same scene in VBR.

[Gary Kleiner]

Logic would seem to dictate the following:

If you have the space, you should use CBR for the best encode because if you set 8mbps as your CBR vs. 8mps as the max for VBR, then some of your material will be at the 8mbps at VBR and the rest will be lower. At CBR ALL of your media will be at 8mbps.

Gary

[Tor Salomonsen]

Frequently, you can see people stating "I've seen somewhere that you should not go beyond 8 mps, because some players may not be able to handle it". Then, you may see statements to the effect of "I've heard that too, but it's never been a problem for me".
I have been advised to set the max at 9.8 mps, the average at 8 mps and the minimum at 0.192 mps. I have done that successfully, but have not tested it on a great number of players.

What I want to know is, will anyone come forward and say "Yes, I have had problems (recently) with certain players and DVDs that were rendered towards or at 9.8 mps".

I suspect no one will, because I think, if the advise was ever any good, it is outdated by now. Those players are so few and far between that to render for them would be like making current computer programs compatible with Windows 3.11.

[Rob Lohman]

Gary: in my experience this is not (always) true with a good
quality encoder. The key seems to be in the multi-pass encoding
where it can evaluate itself. That seems to yield a more efficient
encoding, even at a lower bitrate than CBR.

Personally I've done encodings in the past with VBR with these
settings: 0 - 5000 - 8000 (minimum - average - maximum).

Tor: I think problems with high bitrates are usually due to bad
media instead of the player. All the player should be able to
handle such bandwidth because it does happen on commercial
discs. I can imagine that bad media will have problems being
read at high speeds etc.

[Michael Sage]

I really appreciate the comments in this thread! I'd like to add, that I am not concerned with rendering time or the amount of content that I can fit on a DVD. I only want to render the highest quality content possible within Vegas/DVD Arch. So am I to gather that 8mps CBR will beat VBR?

[Rob Lohman]

It might with their encoder, but it should not in my opinion with a
good encoder. But why not run your own tests? To see what
happens. VBR does not have one bitrate setting, it has three,
so it will also depend on what you set these three bitrates to
as well.

[Rob Easler]

Michael, I myself use vegas to encode for DVD Architect and as stated I am happier with the 8,000,000 rate with CBR because certain scenes show less grain and are definately superior to VBR but my "minimum" setting when using VBR has allowed a low bitrate so as Rob states it will all depend on the settings you use. You will be fine with CBR at 8 but you could easily test a short clip by using the VBR for two passes and just set the min and max and average to 8,000,000 to see if the 2nd pass does anything to increase quality other than taking longer to encode.

[Rob Lohman]

Just to give everyone an idea, I know of people who do 7 pass
VBR encoding in CCE (CinemaCraft Encoder) to get the best
results. With MPEG encoding you should definitely take the time
(both for CBR and VBR). I always keep wondering why people
care whether their mpeg2 takes 15 minutes to encode, 2 hours
or 2 days. I think the end product is more important and I gladly
invest some encoding time for this (not saying VBR is the only
way to go with MPEG encoding or anything).

[Andres Koppel]

My experience is similar to Rob -Easler- I get better result with CBR at 8,000,000. If I compare it to VBR -it doesn't matter which settings I use- , I can see the improvement in both high and low lights. Whites have more detail and break less. Blacks have also more detail. I have also noticed that with CBR the image has less noise. I am talking of a Pal DV original compressed with Vegas Main Concept encoder.