AviSynth should be able to work with any AVI codec installed on your machine. I've used it with CineForm, Huffyuv, AMV codec and UT Codec Pack for HD work. AMV and UT Codec Pack are essentially next generation Huffyuv counterparts coded by competing Japanese coders and are lovely.

Glad you're another x264 convert! Apparently the new Mainconcept h264 SDK is very good, but x264 is free and it's frankly astonishing. What's more it just gets better and better. A lot of people do use it. For example, YouTube uses it for its HD encoding.

Hey Richard, I am frankly shocked at how much better AVISynth is than Quicktime. And to think I stumbled upon this thread purely by accident. Good things happen!

I found that by exporting out of PPro to a YV12 format via ffdshow, I get excellent results (the AVISynth website seems to talk a lot about YV12) when encoding with AVISynth. The results are this. The test is an 11 minute home video shot by an "amature" in HD AVCHD format (Sony Camcorder). It has a TON of movement and shakiness in it, hence the relatively large file sizes. I first exported out of PPro to YV12. Using Quicktime I encoded an 11 minute h264 file (640x360) that required 180 MBs of size to be visually indistinguishable from the original. It did have the expected gamma boost or "white wash" effect. - Using AVISynth, at half the bitrate, I was able to encode the same video to an x264 file size (640x360) of only 89 MBs, no white wash, and it is visually as good as if not BETTER than the Quicktime encoded video. Half the file size, half the bitrate... that is impressive!

I don't know if this is a fringe benefit but the video will play in Quicktime player as well, so as to be more compatible with mostly Quicktime enabled web browsers. I'm impressed, I'm SOLD!