You can specify the Audio Tracks you want (in your case None). Using the example from the help system and modifying it:
In[12]:=
v = Video["ExampleData/bullfinch.mkv", AudioTrackSelection -> None];
Information[v, "AudioTracks"]
Out[13]= Missing["UnknownProperty", "AudioTracks"]
In[23]:= Export["foo.mov", v]
Out[23]= "foo.mov"
The movie now has no sound.
Regards,
Neil
