Virtual sets are a combination of graphics and a configuration file called "config.xml". Take a look into the exemplary virtualsets inside "programms\vMix\VirtualSets\...", especially open the config.xml in a text-editor and examine it, it's pretty much self explanatory.

I'm sorry, but look like I'm not so good working with this, script
could you show me how I can I change the background set...

<?xml version="1.0"?>
-<virtualSet><input dynamic="true" zoom="0.224" y="0.149" x="0.001" name="Screen">a.png</input><input zoom="1" y="0" x="0" name="Set">background.png</input><input dynamic="true" zoom="0.1765" y="-0.255" x="0.005" name="Talent">talent.png</input><input zoom="0.4096875" y="-0.8022223" x="0.005" name="Table">foreground.crop.png</input><zoom zoom="3.818" y="0.942" x="-0.009" name="Close Up"/><zoom zoom="2.313" y="0.081" x="-0.027" name="Medium Shot"/><zoom zoom="1" y="0" x="0" name="Full"/><zoom zoom="1" y="0" x="0" name="Custom"/></virtualSet>

The background of this set is the file background.png. Put your own background image in the same folder, and name it anything you like, e.g. "my_background.png". Then change the filename in the xml-file, like this:

<input zoom="1" y="0" x="0" name="Set">my_background.png</input>

No magic there.

I have to say the main thing I love about vMix is how easily you can add your own titles, virtual sets, etc. With a very low learning curve at that. At least if you have some form of code development under your belt. Heck, all you really need to understand is HTML or XML and just start paying with settings until you get it right. :-)

Even myself never having worked with xaml before, I was able to make a custom lower third in a matter of about 10 mins.