Question : I have been unable to add mp4 files to itune 9.1.

I have been unable to add mp4 files, ripped from DVDs with the program "Ripit", to the itunes 9.1 movie library on my Macbook Pro running OS 10.6.3. . I have tried dragging and dropping the file to the itunes movie window. The file has a green + sign as I am dragging it, but nothing shows up in the movie window.  I have tried adding it to the movie library with the "add to library" command-no luck.I have done as the "Ripit" tech support suggested, which was to option click the file, and set it to "open with itunes", although I'm not sure how this actually helps to import it into the itunes movie library.  Suggestions?
Thanks

Answer : I have been unable to add mp4 files to itune 9.1.

You are right.
http://www.ehow.com/how_5132476_convert-mp-mv.html

"... MP4 and M4V files use the same codecs, which means that they are basically the same file type. Due to this, it is possible to change an MP4 file to an M4V file simply by changing the file extension."