VLC is one of the best video player apps available for iOS. Here's how you can add video files to VLC for iOS via iTunes.
1. Connect your iOS device to iTunes.
2. Click on your device in iTunes.
3. Go to the File Sharing section of the Apps tab.
4. Click on VLC in the Apps list in File Sharing.
5. Drag and drop your video files into the Documents window.
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Additional resources for VLC