CCE File Size: 1 pass vs 3 pass

[jriker1]

I have been creating DVD's with Scenarist and spending a lot of time re-encoding (3 pass) over and over again trying to use up every bit of space on the DVD. I figured after a while that perhaps I would do a 1 pass, see how it fits, and then do 3 passes to make sure everything is clean instead of doing 3 passes waiting for hours and then doing more 3 passes. So I do a 1 pass and find that I have 3 megs of space left on the DVD. So OK cool, that works. Go back to CCE which is still open, set it to 3 pass with the same settings. Go to Scenarist, and tell it to create the DVD. Now it's complaining the file is to big. Does 3 pass make a larger file than 1 pass? Would think it's the opposite since I thought the multiple passes was trying to more efficiently squeeze better quality out of the file with the same bitrate. Thanks for any input on this.

JR

[cinematic]

On the multiple passes the average bit rate will determine the amount of compression, and ultimately the file size. There are good explanations of how to approach deterring the average bit rate. I think there are links to CCE encoding in the Scenarist Re-authoring guides on this forum. First, figure out how much space is available for the main movie after space allocated to menus and sound tracks. Use a spreadsheet to keep track of the sizes; total them up.
You are trying to come up with a figure for average bit rate that will maximize useage of remaining space on the DVD.
Here is the basic formula:

(space available in mb * 1024 * 8 )/ total seconds in main movie = variable average bit rate in kbps

Think in terms of bits/sec. Do a single pass first to build a .vaf file. CCE uses that file in subsequent multi-pass sessions (where you will set the avaerage bit rate). Make sure CCE knows where to find the vaf file in the multi-pass session. You will be able to tell immediately from CCE's estimated encoding time if things are set up correctly. A 4 pass multi-pass session on a 2 1/2 hour movie takes my machine 6 hours or so. I put it to work when I go to bed.

The formula is accurate, but the estimation of how much space is available is not always accurate. I often come up with a final mpv file size slightly too big, forcing another encoding. Save the .vaf file so that you don't have to do the first pass again; just jump right into the multi-pass session. Sometimes Scenarist may warn that the DVD may be too big, but that does not mean it will be.
3 mb is cutting it real close. If you can estimate that closely, you are doing very will. Be sure to wipe out all those files scenarist created when it compiled the DVD too large. Also when you swap in the new, smaller mpv, make sure that Scenarist is using that new file.

[alfixdvd]

Perhaps Videocalc ( at http://www.abelhadigital.com) may help.

[jriker1]

cinematic,

Thanks for the info. I have noticed that the file sizes keep varying so that if you are trying to fit something just perfect on a DVD with practically no space it's never going to be calculated perfectly. The differences between one pass, two pass, three pass, four pass all end up with slightly different file sizes even though the average bitrate is the same. What I figured out is if I do my calculations and remove a few megs from the total filesizes I'm calculating I end up with 4696 or so megs which is pretty darn good and then leaves some buffer room.

Point well taken also on keeping the first pass vaf files. I never did this and may have caused problems. I noticed if you do a multi pass (3) and then do it again, the screen where you can adjust the bitrates manually shows the image cleaner than it did after the first pass vaf file was created (bars are lower than expected for image quality).

The only thing I have left now is to figure out a good formula for how much overhead Scenarist needs. I have a standard menu template for two movies on 1 dvd in PAL format and another one for NTSC. I know exactly now how much they use. However if I need to create a new unique menu, the calculations go out the window as how much space Scenarist is going to use with multiplexing and VTS's, etc is unknown to me. I look at this like DOS. You know each folder and file you create has it's own overhead just for being there in addition to the filesize itself, just not sure what that is exactly.

[PhillipWyllie]

I use an overrhead of about 5% and get no problems. If you write to the very edge of a disc you may get problems reading it in some players.

[bcn_246]

http://www.videohelp.com/calc.htm

I have encoded several hundred DVDs, at anything from CBR 1-pass to 8-pass VBR and have never had a oversized DVD. Just make sure you leave the tracks ISO at 25, don't try and increase quality by reducing it or you may well end up with a DVD oversized by a few MB.

[Trahald]

cce's sizing is definately not perfect, but few encoders are. as someone stated its usually a good idea to leave a little overhead room to allow for this. because encoding is based on quantization , encoders are going to shoot for 'as close as possible' for size. as the quant distribution changes during passes it may overshoot or undershoot size. which one it ends up being is pretty random.

[Sir Didymus]

because encoding is based on quantization , encoders are going to shoot for 'as close as possible' for size. as the quant distribution changes during passes it may overshoot or undershoot size. which one it ends up being is pretty random.

Quoted, quoted and confirmed.

Some time ago I did some test (of course without any intention of generality) on a single cell of a movie ,at different bitrates and with different encoding matrices:

http://forum.doom9.org/showthread.php?t=86038&page=3

You may get a look at the filesize tables...

Cheers
SD