Export alpha channel as a mask?

[Michael Duff]

so you want to export a black and white matte?

import your MOV with the alpha channel … put it into a composition … check the alpha channel is there by turning on just the alpha channel (in the three coloured overlapping circles on the bottom of the composition window). If that’s all good … just render it out again, BUT in the render queue under Output Module change the channels to Alpha instead of RGB. . . done!

[Dnavarrojr]

You da man! Thanks!