Thanks Spot...

Yes, there is quite a bit of motion in the volleyball games I am shooting! And being as how I typically edit the footage in the evening, what better time to render than overnight? So I don't mind a 4-hour render much at all.

I am planning to try version 8.1 as soon as I get Vista 64-bit installed on a spare drive I have in my machine. Maybe the render times will go down somewhat with 64-bits and 8gb ram? We'll soon see, anyway.

By the way--did the bitrate values I mentioned seem reasonable? I believe they are, from the research I've done and the information I have run across.

Thanks again.

TB

I would not set the minimum so low, I've had it cause problems with some players stalling. Around 2Mb/sec is a safe minimum or 1/2 the average. Seeing as how you seem to have enough room on the DVD though the simple setting I use is 8MB/sec CBR. 2 pass VBR is great for when you've got a lot of material to fit and you need to use lower bitrates. Under 1 hour of content 8Mb/sec CBR does the trick every time and encodes faster.
In theory you should be able to go higher than 8MB/sec but leaving a bit of margin below the speced maximum seems to make dodgy DVD players well, less dodgy.

Bob.

Thanks Bob. Aren't you concerned with using a lot of your bit rate on footage that doesn't need 8Mbps though? I am just learning this stuff, so don't get me wrong--just trying to figured out the best way to do this. But the concept of the VBR makes a lot of sense, as does the whole two-pass thing. The 192Kbps is the default on the minimum bit rate in the Vegas template, and that's why I used it. But your logic makes some sense to me I guess--for the same reason as that you wouldn't want to go too close to the upper limit of bit rate on the high end.

I found a website that discussed this a bit and was reading it the other day, and was surprised to see that they said most production DVDs seem to same a maximum bit rate in the 4-5Mbps range. I would have thought it would be higher than that, and maybe it is--but that's what this site indicated.

So I will play around with things on these first few projects. Maybe I will re-render the project tonight using CBR at 8Mbps, just to compare. My render finished just fine in about 4:15:00 overnight, so at least I know I can import, edit & render out the dreaded AVCHD format. (Although I did see frame rates well below the normal 29.97fps value I normally see with DV footage! I guess I'm not in Kansas anymore...)

TB

"Aren't you concerned with using a lot of your bit rate on footage that doesn't need 8Mbps though?"

It doesn't quite work that way. Say you've 20 seconds of static text / graphics. At that point the VBR encoder would drop the bitrate to the minimum bitrate. Let's say that's followed by 10 seconds of furiously fast motion. For a short time it can let the bitrate run at the maximum but then it has to go back to the average bitrate else it'll exceed that total average for the encode and the flle will be too big to fit. The problem is the encoder has no way of knowing what the rest of the footage is going to contain. A 2 pass encode helps it smooth this out a bit more but not by a huge amount.
The very best (read expensive) encoders let you do 100s of passes for this reason. But even so, that only really helps when your average bitrate is low. Realistically the best way to get a good encode is to start with clean footage. I've gone down to 3MB/sec and it still looked OK. But no fast pans or zooms and shot with an expensive camera. The footage had plenty of motion within the frame, it was a football match. The only time the footage looked bad was during the one dissolve I used.

Bob.

"Aren't you concerned with using a lot of your bit rate on footage that doesn't need 8Mbps though?"

What's to be concerned? Are you going to get a refund back from the blank DVD manufacturer on the part of the disc you don't use? Will you make less money if you use up more of the disc?

I would only worry about it if it came to the choice of fitting the video on a single disc vs. using two discs. But if it all fits on one disc, why not go for a constant 8Mpbs?

I'm with Chienworks on this. I don't see the advantage of using variable rates unless disk space is an issue. Is there a good reason not to use the max bitrate?

Dave T2

Great points, now that you put it that way...lol. I am going to try to re-render it at 8Mbps, and compare the results. This particular camera was set up on a tripod for the whole match, so there aren't any pans or zooms at all.

As far as I understand this whole thing, it seems that the only time you would really want to use VBR over CBR is if you were just on the verge of using up the enite media on the disk? If memory serves, the most media you can send to a DVD is about 4.3gb or so...correct? I think I read somewhere that the authoring process takes up some space, but I can't recall how much...but the point is that if you had just about enough footage in a project to fill one disk, maybe then you'd want to use VBR with two-pass rendering to maximize efficiency and pack as much data as you can get on one disk. Not that it'd be a big deal to use a second disk mind you, but it's just that most matches seem to last just about the length of one disk (70-85 minutes).

But thanks for the posts folks--it helps me understand things a lot better...

TB

At some point you might find this very useful:
http://www.johncline.com/bitcalc110.zip

and a thank you to John Cline for keeping this available.

Bob.

Wow! I find it very useful NOW... Thanks for posting the link, and a big THANKS(!) to John (and apparently this Mark fellow, who's name is in the title bar, lol) for putting this together. Extremely helpful to be able to get visual reinforcement of how changing different parameters affects the end result. Outstanding.

I've written several applications in Visual Basic, and this looks like it was fun to put together--besides being extremely useful. Not that is was written in VB necessarily, but I had a lot of fun working with that IDE...more so than the command line stuff I've done in Linux.

TB

I do projects all the time that involve a total running time of 2+ hours.

As others have indicated, there is no reason to go with VBR until you are reaching the 4.38GiB physical limits for a single-layer DVD blank (a lot of us swear by Taiyo Yuden). Or, if you don't mind spending $2 per blank, a double-layer disk with 7.96GiB (Verbatim DVD+R DL blanks seem to be an extremely popular choice).

The benefit of multipass encoding is that one is able to precisely predict the size of the final product; again, not relevant unless you are bumping up against the physical limits.

There are several reasons why Hollywood is able to get away with using low bitrates:

(1) the data is shot at 24fps. Fewer frames per second means a lower bit rate, all other variables equal.

(2) The images in those frames are very clean and noise-free, thanks to high production values and expensive cameras and lenses. Random noise is a worst-possible encoding challenge, so in its absence the encoder can do a great job even at a low bitrate.

(3) A project with a $50 million budget can justify a much more expensive encoding setup than we can, though the quality differences these days are not that great. More money does buy much more speed, however.

One reason I use an encoder called CinemaCraft is because it not only allows for up to 10 passes (I think--never gone beyond 4) but also because it allows one to isolate specific sections of the timeline and manually adjust the bitrate for just that section. For most stuff, however, where you're not trying to squeeze the last bit (ha!) of data onto a disk, the difference between it and the MainConcept encoder in Vegas is small.

By the way, one advantage of going with the Taiyo Yuden disks is that they have a unique glossy inkjet-printable surface called "Watershield." More expensive at about $0.70 per, but the results are stunning.