place quick smoke icosphere over video in video sequence editor I am new to blender and since i am unaware of the terminology i dont know what to search forI have a 'quick smoke' icosphere as a rendered mpeg file.
I have another video in which a man shows his hands as if he is holding the smoke ball.
But in Video Sequence Editor when i add both the clips and add the transform effect to the smoke clip with 'alpha over' and scale it,I get a black box (background) around the smoke.
I have tried to make it transparent as given here
Can Blender render pngs with the background transparent?
How should i display only the smoke without background?
Note:I have also tried changing the opacity of both the transform and smoke strips to no avail
Most video formats do not support alpha channels,at least not the ones built into blender. (there is one option if you are using OSX)

You have two options: 

1.- Export your scene as an image sequence with in RBGA (in a format like PNG, Tiff, TGA, Jpeg2000 or OpenEXR) and then import it into the Video sequence editor to combine your shots

2.- Do the compositing directly in blender either by importing the smoke scene as a strip into the video editor or using the compositor located in the Node Editor