Loading videos to ipod nano 3rd generation

iPod Nano accepts only MP4 format video, please make sure your video is compatible with iPod Nano. If your vide is MP4 video, please follow these steps:
1. Open iTunes and click "File" to add your videos to iTunes library.
2. plug in your iPod Nano to computer, then iTunes will detect your iPod Nano as a device.
3. Select your iPod Nano device on the left panel of iTunes, click "Movies" tab, check the videos you want to sync and click "Apply", done.

If your video isn't MP4 format, you need third party software to convert video to MP4. You may try an iPod converter developed by Aimersoft; it can convert videos to iPod Video and iPod Nano, iPod Touch and iPod Classic with fast conversion speed and excellenrt output quality, that's really good for me, you can have a try, here is its official download link
http://www.aimersoft.com/ipod-converter-suite.html
Hope it helps.