I know when I have a 698 mb video dvdsanta usually make it a 4.3 dvd. How big can a file be in mb before a shrink dvd program can not shrink any more room into a dvd. Like 900 mb or 1 gb? Thanks for any help.

It is not a matter of filesize but a matter of quality. If you accept a greatly reduced quality, then the filesize will drastically decrease.

In general the MPEG format works as follows:

1: store frame 1 completely
2: store only the changes when comparing frame 1 to frame 2
3: store only the changes when comparing frame 2 to frame 3
4: and so forth.

This usually results in a 99% compression compared to a full uncompressed video.
There are two kinds of compression: lossless (no reduced quality) and lossy (reduces quality).

DVD Shrink uses a technique to re-encode the mpeg format into smaller mpeg. This will reult in quality loss (usually noticable on black backgrounds with dark, fast moving items).

In theory you can shrink to infinity, but after a few steps the quality would be horrible to such a state that it's not watchable anymore.

It's also a factor of the length of the video. A movie of 90mins will convert with very decent quality to a DVD but the quality will be significantly reduced if the movie is 180 mins.
Also the type of movie can be a factor. Animations convert very well but movies with a lot of high speed action and/or colour tones will probably suffer more.