[Mabel Lau] "I re-examined my timeline and found that all of my clips are in PR422 codec except for one super which is in Animation codec. My timeline is HDV 1080i 50"
Why is your sequence HDV?
Unless you intend to print to HDV tape I see no pint on doing that.
Beside slowing down rendering that will degrade your picture: High compression and geometry transformation (1440x1080).
rafael
http://www.nagavideo.com