Optimal average bitrate for VBR?

[Matthew]

Now I use an audio bitrate of 224, with 1 audio track. Under these circumstances, the video bitrate can only go up to 2400, after which there is a risk of freezes, stuttering and the like on my dvd player.

Anyway I have some choices to make about the number of cds to use on particular films. e.g. for a 140 minute film should I use 3 x 80 minute cds or 4 x 74 minute cds?

With 3 x 80 min cds, the max bitrate would be 2400 and the average would be a little above 2000. I'd use 5 pass VBR.

With 4 x 74 min cds, I'd just use 2400 CBR.

Would the quality on the VBR rip be as good as that of the CBR rip? And more generally, how low could I go in choosing a minimum average bitrate that provides the same quality as a 2400 CBR rip? I know it depends upon the film, but for most films, there's plenty of scenes without high action.

Thanks for any advice ;)

[mrbass]

4 pass vbr at 1800 or 2000 would look better IMHO (DDogg isn't around to defend) than a 2400 CBR. Only reason to do CBR is for a quick encode and if you don't mind the extra cds 3 or 4. Just keep it about 1600 VBR for great results.

[Matthew]

Correct me if I'm wrong, but that doesn't make sense. Unless I'm mistaken, VBR is only different from CBR in that it allocates less bits to those frames with low motion. That's why it takes so long. Hence a VBR rip with a max bitrate (not average bitrate) of XYZ can only ever be equal in quality to a CBR rip with bitrate XYZ, never better quality.

Well if it looks as good, then I'm happy, but your response (re DDog) indicates it isn't cut and dried :(

BTW did you check up on that chapters thing?

[Kedirekin]

I agree with Mathew, a CBR encode at 2400 will look as good, or maybe even a little better, than a VBR encode with a max of 2400. To clarify, CBR might look better in the portions of the movie where VBR drops to a low bitrate.

I'm sure a lot of people will disagree, but even they must in fairness agree that the difference would be small.

[Matthew]

Originally posted by Kedirekin
To clarify, CBR might look better in the portions of the movie where VBR drops to a low bitrate.

Well that's the thing I'm worried about, but surely if the average is high enough then the difference isn't discernable? Some scenes just don't need a high bitrate. So the question is which average will suffice for those of us who are anal retentive about quality ;)

[mrbass]

well the thread no longer exists cuz it was on the old board. But basically IIRC DDogg tested and said something like 1800 3 or 4 pass VBR was equal to a 2400 CBR with Temporal Smoother. DDogg was the one who got DVD2SVCD to add it as an option. Note though that temporal smoother slows it down 40%. If DDogg comes back he'll clear it up again. I ain't gonna argue CBR doesn't look good but your bitrate should be at least 2200 or above.

[markrb]

I remember several old threads about CBR vs. VBR.
What I got from those threads and makes the most sense to me is that a CBR of equal value to the max of a VBR will be no worse and there is a slight chance it could be potentially better.
What VBR gives you is a better way to save precious disc space. If you took a CBR of 2500 it would take much more space then a VBR of 2500 max, because the only sections that will reach the max value are the complex scenes. Black screens, credits, little motion and other low complexity scenes may look just as good if encoded at 300 or 2500. Why waste the bits and thus space?
Now if your video will fit into the specified number of disks you want regardless of bitrate go ahead and use whatever you want.
CBR will encode faster because there are many fewer calculations going on. CCE is simply reducing the bitrate of the VOB file to a constant value that never goes lower.

The slight kicker here is that mpeg2 specifies VBR. It can be made to do a form of CBR, but it was developed with VBR in mind.
The opposite is true for mpeg1. It was developed with CBR and can be made to do a form of VBR, but very limited.

In the end if you want to make the best possible encode fit on the fewest discs use a high pass VBR.
If you want speed and disc space is not a concern use CBR.

If you are concerned about encoding speed use a 3 pass VBR. I haven't found anyone that can tell the difference between 3 pass and higher. I only use 5 pass, because I can do an entire encode of most videos in 8 hours or less. Basically when I am sleeping. When I had a slower machine I always used 3 pass.

mrbass I know that DDOGG often talked about using 1 pass VBR with TS. I don't remember anything about CBR and TS, but I could be wrong.

Mark

[Matthew]

Thanks for all the comments. I wouldn't want to do a CBR rip with anything other than 2400, otherwise I'd use VBR. e.g. the 2 rips I've burned are VBR with an average bitrate greater than 2200. Anyway, it looks like I'll opt for VBR with a 2000 average bitrate in the cases I'm thinking of.

mrbass, what's the temporal smoother? I assume it improves the quality of a CBR rip?

markrb, I'll probably stick with 5 pass because the machine is fast enough ;) 4 passes at a minimum.

[Mozart]

you can try robshot's method also. Firstly, do a full encoding with DVD2SVCD setting CCE as 1 pass VBR with Qfactor = 70. In bitrate tab turn on min avg equal to 2400. Set max avg = 2400 also. This will skip the internal bitrate calculator.
After the end of DVD2SVCD work, follow the 2nd step (http://www.robshot.com) of robshot's method. Here you will need to use a bitrate calculator. After this, use crash recovery to restart from muxing and cutting (or pulldown). As you can see, this is not for newbie:D