Anyone know how to create light trails on a video?

Can't figure it out.. Maybe not possible?
I have after effects, sony vegas, flash..

In After Effects, I believe it is called 'video echo'... That is a good place to start. Then if you can matte out everything but the color range that the trails are making, and layer that back on top of the original video, so that only the trails get blurry!

-Alien Jon

I've not used flash for a while, but can you actually put the onion skin tool on the actual video? Cause that would be similiar (but cooler!) that what you're after.

Great.. It worked alright in a quick test.
So..

I duplicated the original layer
Then applied time echo to that layer - settings (echo time 0.02, number of echos 9)
Then colour keyed any red bits and other background bits out.
Then set layer blend mode to screen, and layer opacity to 80%

Thanks!

This would make a great arcl;e if someone could flesh it out a it more I've been wanting to do this for years