So..... I figured it out.
1stly, I deleted all the movies in iTunes on my new Mac that encountered "this movie requires quicktime not supported itunes" error when I try to play them.
When prompted, I just "Delete" the movies permanently.
I figured we don't need to "Keep" these corrupted files.
It just take up space in my also precious external drive (Time Capsule) for nothing.
Then, I use my iTunes on my iPad to download all the movies & TV that I bought previously that has "this movie requires quicktime not supported itunes" problem.
I make sure I am NOT requested to "Buy" or "Rent" when I try to download the movie/TV.
It should be "Download".
If the "Download" selection is not avail, I probably had selected the wrong movie/TV in iTunes on my iPad.
(Do take note some movie may have the same titles but some are Extended version or Director's cut that you didn't purchase previously)
After all the downloads on my iPad are completed, I hook my iPad to my new Mac & transfered all the downloaded movie/TV into the iTunes on my new Mac.
Right click to "Transfer Purchase from XXXX's iPad" will do it.
All my newly downloaded movies/TV appeared on my Mac's iTunes.
And I can play them without any more, "this movie requires quicktime not supported itunes" error.
I can even transfer them to my iPhone using Sync on my new Mac's iTunes just to make sure nothing else is wrong.
Note: Make sure WiFi is fast & no one turns it off when iPad is downloading.
WARNING: If your iPad is on cellular network, do remember to turn it off if your are on limited data plan wirh huge data charge for exceeding the limit.