The topic is to hard to explain I think based on your understanding on of video compression.

I would start by reading the Help Manual and focus on match media button to set your project settings.

Then read about render profile settings and the = sign that appears next to them.

Basically MPEG or MPEG 1 is not really used anymore, so you would need to determine what level of MPEG2-4 your video is compressed with. A free app called "Media Info" can be downloaded that will tell you the details of your file.

Then you need to render your project out to a render profile that matches or exceeds the bit rate of the encoded original file in the same MPEG specification. That will give you a very similar look to the original. Non-destructive / No Recompression editing is not really a thing anymore, and is hard to get Vegas to do.

If you know command line well, you might be able to snip out what you need with FFMPEG, and get a no recompression copy of the file.

There is an application (not free, but reasonable) called VideoReDo, which does just what you’re asking for. Take a look at it.

I wish to express clearly Sir. My video man records in .mts format in his videocam (for example, a 3 hour concert may be in more than 100GB in .mts format) and after editing in his Adobe Premier, he gives me an MPEG-2 version of 32 to 35 GB of the same 3 hour concert. Now I take it into the timeline of my Vegas Pro 14 and cut some more unwanted portions of video. Now I wish make it two equal pieces so that I can make two DVDs of 4.7 GB each so that quality is not bad when I give a DVD of the same. Here what I understand is, I will make it into two pieces but cutting in the centre. And select first part and render it to burn disc. If this is ok, and after that, I select the second part and render to Burn Disc. Then I am not able to understand, why DVD Architect is supplied to me alongwith Vegas Pro 14. Please enlighten me Sir.

As I see it you have a 3 hour concert which you will edit/trim and the final product will be 2 DVD’s holding 1.5 hours each.  Vegas will render out the necessary files ready to pass onto DVDA for burning. 
Some compression will be required to fit 1.5 hrs onto a 1hr DVD.  VP14 does not output files that can be
directly burnt to a DVD, hence the need for DVDA

A second problem is that DVDA7 as supplied with VP14 does not handle/provide .AC3 Dolby Pro and VP14 cannot export .AC3 pro.(unless modified as detailed on this forum)  You are faced with degradation all be it minor.

Would be inclined to make a test DVD and evaluate the result.  It may be OK. If so job done.

thankyou Sir for your great advice. But after I put an mpeg2 given by the camera man to me, on the timeline of VP14, then when I open Render As, there I see in the list a line BURN DISC. If I click on it, it is rendering .vob files as required. Did I say anything wrong Sir or Am I troubling you with my innocency. Please don't mind sir.

A lot of your problems are solved if your client would accept blue-ray instead of dvd, keep output size to 23.1gb or less for single layer (25gb discs), if bigger then use DL (50gb) discs, and the quality is a lot better. You can do this all within VP14, save to iso first, then burn copies.

The maximum size for material on dvd5 is 4.35, not 4.7 GB. That has to include audio and menus as well, so don't overstuff the media.