Converting Between Colorspaces
Most formats intended for distribution, like DVD, VCD, or various MPEG-4 variants use the YV12 colorspace because it takes up the least space. AviSynth also works in this colorspace. This doesn't cause any problems most of the time, but once again CCE is a little different. CCE will only accept video in the YUY2 or RGB colorspace. Depending on which codecs are installed on your computer, one may automatically convert for you when you open an AviSynth script in CCE. However, it's better to do the conversion yourself at the end of the script.
If you're not familiar with colorspaces you can get more information from our Digital Video Essentials guide titled Color Formats.
AviSynth CommandsThis is another filter that needs to know if your video is interlaced.
Placement In Your Script
Colorspace conversion is normally only done at the end of a script or immediately before some external plugin that doesn't work in YV12. When you're going to be opening a script in CCE make sure to put it at the end. If you're going to be opening it in any program that can handle YV12 video don't worry about adding this line at all.