encoding from a non-preset ratio source

[gain]

I've been following major's VIDEO_TS->DivX guide for some time now attempting to understand how ffmpegX determines frame size and bitrate and have two questions:

1) how do set up, say, the preset for DivX mencoder to do 1.78:1 conversions? I typically set the preset to 1.85:1 and follow major's guide. I then break out the calculator and determine, on my own, the height for 1.78:1 based off the auto calculation of the width ffmpegX gave me for 1.85:1. I do that by taking the auto-calculated width and dividing it by 1.78. This seems to work and results in very near the correct aspect ratio in playback, but, I'm guessing, because I change the auto-calculated results to get the correct aspect ratio, I loose my "fit too" MB size... the resulting avi file is always quite smaller than my requested 700MB filesize. Is there something I'm missing to do this automatically? I typically do 2 pass encoding with all the "high quality" presets described in the guide engaged.

2) Using a source with an aspect ratio of 2.35:1 (holds for 1.85:1, etc.) and following the aforementioned guide, ffmpegx never calculates the video size correctly to result in a 2.35:1 aspect ratio in the resulting avi file. I usually hit "Auto", let it do it's thing and then take the width and divide it by 2.35 to get close to the source aspect ratio in the resulting avi... resulting in less "squeezed" looking end product. Of course, this seems to affect my end result avi filesize. Why is the calculation off to the point of it being noticably squeezed? Am I doing something wrong or missing something here too?

In both cases I can never get ffmpegX to generate a file that is close to what I want in terms of filesize. It is usually of by 50-150MB... almost always right arount 150MB smaller than what I set. In all cases I am using CBR MP3 audio and 2 pass encoding. I've tried both the mencoder DivX and XviD.

Am I being to anal about getting an avi with as close to the original aspect ratio as possible? I want to use all of the filesize to achieve the best looking video.

Hope the 1.78:1 subject hasn't been covered. Apparently you can't search for just numbers like that in this forum. I've seen discussion of the filesize, but haven't located any good answers yet.

Thanks a lot for any help and thanks, major, for a really cool piece of software.

[gain]

Followup: I am, currently, trying to convert a 1.78:1 source file to avi. I followed the guide and did an auto-crop then an "Auto" with a framesize of 16:9 just for kicks. The resulting, auto-generated aspect ratio is 560x304 -> 1.8421:1. This would be cool if the source was 1.85:1. I could live with that! But it isn't very close to 1.78:1.

I'm beginning to wonder if, even though the source is marked as 1.78 it might not actually be or the source has some black bar padding and the auto-crop and "Auto" size functionality is actually doing it's job just fine.

UPDATE: this encode just finished. The final file size is 250MB though I chose 350MB in the bitrate calc area of ffmpegX before hitting Auto.

Why does this bamage my drain so much?!

[major]

There is no 1.78:1 choice in the Autosize popup, but you can set manually whatever aspect you need by simply defining width and height. If your target width is 560, then divide it by 1.78 and round it to the nearest value divisible by 16 (320). You may do the same to check whether current values are good for any other aspect ratio.

About the size issue, I would need more detail and possibly a copy of the files. You can email me to major4@mac.com.