I meant a USB pen drive. Well NX500 supports only 4GB drives. I think there's a problem with the encoding because I get the stutter while playback on PC too. What encoder do you use? I use Xilisoft Ultimate.
I use Video Converter for Mac - http://www.videoconverterformac.com/
I paid US$35 - Around Rs.1,750. But, its totally worth it. It encodes into every possible format available now. But, if you're using Windows, I ain't sure of which one would be the best converter...