Online FLV Video editor

I am trying to make a very scaled down version of these applications:

I have been looking at ways of doing this but can find nothing. Jumpcut seems to be creating a FLV on the fly. Can you export an edited FLV from Flash 9? I would imagine you would need to use something like Ffmpeg on the server to complete the render.

If anyone could point me in the right direction for starting this project that would be great. The application would need to include png overlays and the adding of soundtracks.

I can find no details on doing this, the closest i have come to is a really cool air application created by Benjamin Dobler, but I am not sure if he is using features in AIR to do this.

Thanks Alex