It's easy to play YouTube with iTunes by converting YouTube .flv files to iTunes video.

1. How to play YouTube with iTunes?
iTunes is a popular video player for Apple users, no matter on Windows or Mac. It can play any
media files that supported by QuickTime, like MP4, MOV, M4V, DV, MPEG, 3GP, MP3, WAV,
AAC, AIFF, etc.
What video files work with iTunes?
Video content purchased from the iTunes Store.
QuickTime and MPEG-4 movie files that end in ".mov", ".m4v", or ".mp4" and are playable in
QuickTime Player.
Video podcasts.
iTunes Digital Copies.
iTunes Store Movie Rentals (Requires iTunes 9 or later).
As you can see, YouTube video is not supported, so maybe you wonder how can I play YouTube
with iTunes. Playing YouTube with iTunes is easily achieved if you convert YouTube to iTunes
supported movie types. Below are two software recommended.
http://www.youtubeconverter.org/play-youtube-with-itunes.html
Play YouTube with iTunes for Windows:

2. iOrgsoft Video Converter is an all-in-one software for converting almost all common video files to
iTunes video, or convert to Apple MP3/MP4 player for watching on iPod, iPhone, iPad, and Apple
TV. After converting YouTube to iTunes, you can play the YouTube files smoothly on iTunes or
sync them to iPod, iPhone, iPad for enjoying wherever you go!
Play YouTube with iTunes for Mac OS:
Doremisoft Mac Video to iTunes Converter is designed specially for Mac OS users converting
video files to iTunes video, which supports change YouTube to MP4, MOV, DV, and 3GP that are
used frequently by iTunes. You can also extract YouTube audio track to MP3, WAV, AIFF. Free to
try the software.