Is it possible to change a video file so that it becomes an angle of the main video file & if so how is this done?

Not sure I understand - an angle of the main video? Do you mean to keep one angle of the multi-angle video? If so, there's a "Strip angles" option at the VTS level.

A while back I authored a travel DVD for some friends & knowing that some had 16x9 & others had 4x3 screens so I rendered out the same video file in the 2 different ratios. My main menu offered 4 choices Play All or Scene Selection in 16x9 ratio & the same options on 4x3 ratio. I had 2 almost identical sets of scene selection menus. The only difference between the 2 was the shape of the animated thumbnails. All of this DVD works correctly as far as it goes. It was created using Sony Vegas & DVD Architect.

I have since seen my first DVD that used the angle features that are available to DVD players. Using this feature when playing back a DVD you just would press the angle button & it could switch between the 2 ratios on the fly rather than having to go through the menus. The 2 video files are exactly the same length & share the one audio track. I realize that had I been authoring this DVD I would have created it using the angel feature rather than having 2 sets of scene selection menus. I was just wondering if its possible to use this program to alter my DVD so that angles are used to switch between the 2 ratios.

Your DVD is not multi-angle then because you cannot mix the 2 ratios in the same VTS.

How does your main menu offer 4 choices in both 16:9 and 4:3 ratio? You can have only one or the other. I think you mean you have a menu in 16:9 in one VTSM and another similar menu in 4:3 in another VTSM, correct? Actually, you just need to create only a 16:9 pan/scan menu. This way, if viewing on 16:9 TV, the menu will be displayed as 16:9. If viewing on 4:3 TV and the dvd player's setting is 4:3 letterboxed, the menu will display as full screen with both left and right side cropped, where there is no important information is shown on the side.

You can make use of the angle button on the remote as a switch between wide screen and full screen versions. Each version will be in its own VTS. Define one of the menu PGC in each VTS to be an Angle menu category. This menu PGC will be called each time you press the angle button. Write a pre-command to jump to one of the VMG PGC and redirect to the appropriate VTS version.

I don't know the details of Vegas and DVDA capability, but they may be able to do this. Certainly, DvdReMake Pro is able to do what you're asking.

You ask how my main menu can offer 4 choices in 2 different ratios. The 2 MPEG2 files were rendered in Vegas as both a 16x9 & 4x3 files. The 2 files really are different since they were cropped differently. When these files were imported in DVD Architect I then set the authoring projects to 16x9. The original 16x9 file displays full screen 16x9. The 4x3 file displays 4x3 but with black bars at top & bottom. This may not be the correct way to do this but the 2 different ratios display correctly when each option is selected.