Thanks purplemonkey369.
I download the software, and go to File\MPEG tools.
Then I choose the "Merge & Cut" tab.
After adding the 2 files to merge and keying the name of the output file name, I hit the "run" key.
Even though the 2 video files are from the same settings and from the same v-cam, and there are sounds in the 2 video files, there is no sound in the output merged file.
Do you know how to make the merged file contains the sound?
Thanks.