Some users have reported an issue in which various media, such as movies, music and podcasts, ostensibly sync to the iPhone, iPod or iPad but fail to show up on the device after the sync process.
- Connect to a different computer. Some users have found temporary respite from this issue by connecting their iOS devices to a second Mac or Windows computer, but not choosing to erase when presented with the “the (device) is synced with another iTunes library. Do you want to erase this iPhone and sync with this iTunes library?”
- Reinstall iTunes. In some cases this issue can be resolved by completely removing then reinstalling iTunes as described in this Apple Knowledge Base article.
- Remove third-party backup software. If you’ve installed software for an external hard drive or another device, it may include an automatic backup utility that recognizes the device as a storage device, interfering with the normal sync process. Try uninstalling any such software then re-syncing your device.
- Delete iTunes .plist. If you’re using a Mac, delete the following file
~/Library/Preferences/com.apple.itunes.plist then restart