Bit rate calculator? Is it true or false?

[help96]

In pursuit of the perfect DVD, I have now managed (by accident that I have yet to understand) to encode 130min to a DVD using ffmpeg with the sound in sync. The problem is that the bit rate calculator seems to be desperately erroneous, leaving me with a very differnet file size than the one desired.
I have the manual backwards and forwards and even if it is very clear, I seem to be missing the finer points.

I set the video parametres to 4GIG DVD, the time to 130min and click the general settings to pal DVD low quality. It gives me a green bit rate figure (which seems never to be the same each time). I am not interested in the finer points of the quality, but only wish to have the 4gigs filled with program. I encode file and many, many hours later I get a load of files with a .bin. FANTASTIC. except not because my .bin is only 1.3GB and the result looks lke a QT movie from 1986.

Firstly, is there any real correlation between the Bit rate calculator and the result video presets? I preume it is a guesstimate.
Secondly, why do simple programmes like idvd limit the file size and is there anyway of mixing your fatastic invention with their?
Is there some 2 pass method or a simple bit rate ceiling to pack the stuff in ?
Thank you

[major]

The bitrate calculator assumes that you're encoding in constant bitrate mode (DivX, XviD, VCD..). In case of VBR encoding like DVD there is no way of predicting the final size before encoding, as the bitrate value will vary continuously depending from the video spatial and temporal complexity and the Qmin compression value. I would suggest you to use the High quality preset and to finetune the bitrate after testing the filesize on a small chapter.

[help69]

thank you mister major (where do you find the time to live if you're not answering question?)
I presume that to resolve my problem, for practical purposes, I should encode as a SVCD in high quality so that I can optimise my disk space and not have to do hundreds of tests. My dvd player seems to read VCD but is this encoding possible on a dvd and is the codec worse or different to mpeg2 DVD? Personally, I don't care if it is DVD, VCD or vinyle as long as it works in 4gigs and does look like QT circa 1986.