v.attachalpha v.attachalpha adds an alpha channel to the incoming video stream. v.attachalpha adds an alpha channel to the incoming video stream. If a stream is being received in the second inlet, it is applied as the alpha channel. Otherwise, the alpha channel is filled with 255. The alpha channel is used in a number of objects (particularly v.composite, v.screen and v.window) to mask or mix streams. Objects that manipulate the spatial characteristics of a stream (i.e. v.zoom or v.flip) will also process the alpha channel if it exists to maintain a lock between the stream and its alpha channel.

from the library : softVNS Format : External Environment : jitter / max commercial Max 4.x http://homepage.mac.com/davidrokeby/softVNS.html