iTunes: May be unable to transfer videos to iPhone, iPad, or iPod

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iTunes can play a wide variety of video formats. However, iPhone, iPad, and video-capable iPod devices play videos in specific formats. Any music video, TV show, or movie purchased from the iTunes Store is designed to play on the iPod, iPad, or iPhone and can be easily synced with iTunes 9 or later. 

The iPad and iPhone 4 can play High Definition (HD) content and Standard Definition (SD) content. iPods and the original iPhone, iPhone 3G, and iPhone 3GS can play Standard Definition (SD) content. To find what video formats are supported, see the Tech Specs page, click your device's product family, and then your specific model. All HD purchases from the iTunes Store also include an iPod/iPhone-compatible Standard Definition version to accompany the HD version. When syncing an HD purchase from the iTunes Store, iTunes will automatically sync the SD video for devices that require SD content.

Video podcasts

Even if you download video podcasts from iTunes, individual video podcast authors usually provide video podcasts, and in some cases, these podcasts may not play on your device. If the podcast is correctly encoded however, it will sync to the device without issue.

Other video sources

If you did not purchase videos from the iTunes Store, they may not be in a format that you can play on your iPhone/iPod. In many cases, you can convert them to the correct format using iTunes or QuickTime. 

• Using iTunes: Select a video and choose Advanced > Create iPod or iPhone Version
• Using Mac OS X v10.6: Open the video in QuickTime Player and choose Share > iTunes and then select the iPhone & iPod option.
  

If you're using a Mac with iLife installed, you can also use iMovie to export a movie in an iPhone/iPod-compatible format. For questions on choosing the correct format, refer to iMovie '11: Choosing the correct export option for your iPhone or iPod touch.