Rendering Video with transparent Background

Yes it is! For starters, make sure your comp actually has a transparent background, not simply a black background, by toggling "Toggle Transparency Grid" button at the bottom of the comp viewer (it's the small, checkered button). If the background changes to the checkered pattern, you're good to go.

The only other thing to deal with is the proper output settings. Not all codecs support an alpha channel. I typically use these settings in the Output Module:

Format: Quicktime

Format Options
-Video Codec: Animation
-Quality: 85 to 100, depending on how critical quality is. 100 is uncompressed.

Channels: RGB + Alpha
Depth: Millions of Colors+ (the "+" indicates the alpha channel)
Color: Straight (Unmatted) - This avoids a luminance shift in semi-transparent areas that you get with "Premultiplied (Matted)"

Others use TIFF or PNG image sequences instead of Quicktime Animation, but the underlying concept is the same.

Hope this helps!
Josh

You're quite welcome! You might also be interested in downloading the free Knoll Unmult effect, which is perfect for creating transparency on items where you would normally use "screen" or "lighten" blending modes to see the underlying layers (such as a lens flare applied to a black solid). It creates an alpha channel based on the luminance of the layer, which is very handy.

Enjoy!

This has helped me so much. Thank you!