Alpha channels in After Effects

[coverrn]

What is the easiest way to build an alpha channel in an animation (in After Effects)? Are there instructions for this? I tried several different ways of adding alpha channels, mattes, and color keys to my timeline layer but when I rendered the alpha as a matrox mjpeg the final file looks all white.

[Sparky]

Alpha channels in After Effects are inherent to the animation process. In other words, you don't need to make one, it's made automatically. You just need to setup your output module correctly. For use with the Duet what you need to do is under composition (menu) choose add render module. Click on that render module in the render queue and choose alpha from the channels drop down and then name the file the same name as the fill with .matte at the end. The Duet clip player will pair the fill and the matte together. (This is using Matrox Digisuite). Now some codecs support alpha, in which case you can choose Channels: RGB+Alpha, Depth: Millions +, Color: Straight.