Digital Workshop

I've got a video that I want to use as a background. It's 30 Seconds long and currently a really big MOV file. I'm taking it into After Effects to do a bit of work on it and then I need to output it to be used full screen as a background on a 1024 x 768 presentation. What format is best to output ? Thanks...

I can't comment on the format but I think you're asking for trouble attempting to play video that size. - Producing a video at that resolution is going to tax even a fast PC.
I think the only way you will get reasonable playback to to produce the video at a nice integer multiple (like a quarter of the screen res) and scale it - scaling is easy and most video cards can do it well. Decoding compressed video is hard and the more of it there is, the slower everything else will be.

I discovered that Adobe Premiere has an MPEG encoder so I exported my Video from After Effects as a MOV and then imported to Premiere, exporting as a MPEG-1 for VCD. It worked a treat. The video size is 720 x 576 and scales up fine. I wouldn't dream of making it 1024 x 768! Its just the presentation that's that size!

The output file is 35 seconds long and just under 5 MB.