I haven't done a lot of video recording with my 5N, and it's not a media I'm too familiar with. However, I did notice a slight stuttering on parts of your movie (and in some of mine too especially when I pan).
I'm wondering if the speed type of the memory card have is not fast enough for HD video and could be lagging behind?
I also found the info below from the 5N handbook... mostly gibberish to me, but you might be able to find some clue?
The AVCHD format is a high definition digital video camera format used to record a
high definition (HD) signal of either the 1080i specification1) or the 720p specification2)
using efficient data compression coding technology. The MPEG-4 AVC/H.264 format is
adopted to compress video data, and the Dolby Digital or Linear PCM system is used to
compress audio data.
The MPEG-4 AVC/H.264 format is capable of compressing images at higher efficiency
than that of the conventional image compressing format. The MPEG-4 AVC/H.264
format enables a high definition video signal shot on a digital video camera recorder to
be recorded on 8 cm DVD discs, hard disk drive, flash memory, memory card, etc.
Recording and playback on your camera
Based on the AVCHD format, your camera records with the high definition image
quality (HD) mentioned below.