My encoder refused to be set lower than 4:4:4. And the codec could not be used in After Effects either. Someone gave me the 7 version. That works better. But my initial problem still remains: the XPression bleeps and prepares very long before playing. Something is wrong and I can't find it.
FYI, There was a bug that if you have a video clip on a scene director track and the clip starts in negative time (the video on the track is dragged to the left of frame 0), then it will take a long time to prepare. This would not be affected by the video coder or the clip itself.
#XPression