I'm also facing the same problem. I can not add .MP4 files (videos) to my iTunes library or play through it. I have no problem in adding .MP3 files to the library but have no success with MP4 files.
I tried "Add file to Library" and also tried to directly drag and drop in the main iTunes window.
I have even tried to copy the .MP4 file to 'iTunes Media' folder to no avail. I can not even add the file to the 'Automatically Add to iTunes' folder within 'iTunes Media'.
Ipod Touch 4, Windows XP, iTunes10.6
I had this problem as I was trying to drag and drop video files into the "films" window in itunes. I got it to work by dragging and dropping a video file into the "music" window. The video then suddenly appeared in the "films" window and thereafter I could drag and drop my other videos into "films". Let me know if this works for you too!
Apple is getting worse by each day and they are trying to get rid of the user fiendly and free stuff just outside the window!!!
its not working because of the specifications of the MP4 format...The bigasoft (convertor) is also not a freeware what i would suggest is get the idea of the format of the videos and use a freeware to convert the videos to the required specifications.
nothing changed for me also . . . running win-xp . . . itunes had previously functioned fine . . . updated itunes . . . mp4's stopped viewing (thousand-lines inside viewing window ... only hearing sound).
tried redoing the mp4 file . . . tried repairing quicktime via ctrl-pnl / sftwr . . . tried unstl / rnstl quicktime . . . nothing works.
went to apple's website . . . in the end, 188.8.131.52 installed instead of 7.7.2 . . . go figure.
this about wraps it up for me . . . since apple is becoming more 'n more proprietary (communistic) . . . i will simply stop using all apple® products . . . apple® fails to realize who brought them greatness . . . down with apple® . . . this seems to be the only language apple understands.
(edit) . . .
even if i would use another program to convert / decode or whatever . . . itunes next release will nullify the hack.
I had this problem toooooooooo
First right click on the mp4 video that u want to add
Open with-->Quick time Player
Sometimes some of Quick time player's file will be used by itunes
when you open a video using Quick time Player,it'll fix the problem
now drag and drop the video to itunes, it'll work fine..