Most video recording devices have a limit on how big the file size can be. Your video probably exceeded that limit, and so the camera stopped recording to the first file and started a new one. If you are using a Windows computer, believe it or not, there is a Windows command that will stitch them together. Put the files in the same folder on your drive. Open a command prompt and navigate it to the folder where your files are. If you're not familiar with DOS commands, let's say you have your videos in a folder on your C: drive called Videos (or in other words, the C:Videos folder). When you open your command prompt, you will type the following command to navigate to that folder:
Be sure that you use a and not a /. Now let's say your files are called video1.MVI and video2.MVI. You will use the following command to stitch them together:
copy /b video1.MVI + video2.MVI videofull.MVI
On the flip side of what I told you earlier, be sure to use a / and not a in this command. Instead of videofull.MVI, you can use any name for the new file that it will create. This is just an example.
If you have a Mac, I heard from a Mac user friend of mine that there is a similar command on the Mac, but I don't know what that would be off the top of my head. I believe it is a "cat" command. You can probably Google it, though.
I hope this helps.