We have tried several options for keying text over video and for the cost, we have not been able to beat using Easy Worship. We feed in video from our Edirol presentation computer via an s-video input card (as recommended by EW) on our presentation computer and then use EW to place the text on the video and output the whole thing via VGA to our projectors. The quality is much better than typical keyers due to the fact that EW allows us to shadow and outline the text (whereas the keyed text looses all that info and just shows the text letters with a rough edge). I know there are better keying systems out there, but for the cost of EW and a simple s-video input card (about $40), we just can't beat it.
