Adding my home video DVD's to the Duo for streaming

This simple concatenation works and preserves the true original format:

Using the Windows copy command: Because the VOBs are simply split files created from previously contiguous larger file, you can reconstruct the larger file using the window copy command. To do this:
a) Open a cmd window using the Windows run command.
b) cd to the folder containing your VOB files.
c) At the command line, enter a command similar to:
copy /b vob1.vob + vob2.vob + vob3.vob outputFile.mpg

This will concatenate multiple VOB files into one output file. Note: Please don't forget the /b switch.

You have a special case, with lots of content that you recorded yourself on a specific DVD recorder. While straight concatenation might work for your content, it will not work in general.

In a commercial DVD, the .IFO file is what contains the navigation information for the DVD - it essentially includes an index of the VOBs which acts as a seamless playlist for each title on the DVD. Playback of the VOB files is often not sequential.

One example is the Disney movie Wall-E. That particular movie shows computer screen printouts in places. The language is matched to the sound track (so someone listening in French also sees computer screens in french, if you are listening in English you see screens in English). The way this kind of thing is done is that every time computer text is shown, the DVD jumps to the part of the VOB file for that particular language. When the text is finished, it jumps back to the mainstream.

Often times there are extended cut and regular versions of a film on the same DVD. This is done in a similar way. The common parts of the movie are only on the disk once, and are shared between the two titles.

Also, there are previews, etc. In some cases they are in their own VOB file, in others the main movie and the previews are mixed into the same VOB.

If you don't have an IFO file, your method is all you can do. But the correct way to recombine the VOBs is to use a program that reads the IFO, and extracts the media from VOB for the desired title in the indexed order. There are lots of rippers that can do this.