In that particular clip I didn;t use a video matte. I simply applied a 'Motion Blur Camera Lense' filter to the monochrome video. It was by sheer chance that the halo effect appeared. However Mediastudio does have full video matte support. The best place to start with Mattes is to check our the excellent tutorial (using Video Paint) in the manual.
As for muting sound within your project, try the following,
1. On a clip by clip basis, select the clip > right click clip > split audio > then simply delete the audio on trach Va or Vb (or where ever)
2. On a project basis you can mute the sound on an entire video track simply by unchecking the 'enable / disable' checkbox on track Aa, Ab, A1, A2 etc etc as appropriate (the 'enable/disable' checkbox is the checkbox on the left most side of the timeline)
3. To use your own audio all you have to do is insert your audio file onto track A1, or A2 or whatever. (Insert > Audio)
4. Enjoy
