Sounds like dropped frames.
Something is slow.
The usual cause is using a slow memory card.
You should be using a SD memory card with a speed rating of "Class 10" or an x-Rating of "66X".
You can read-up on memory card speeds at this location:
http://en.wikipedia.org/wiki/Secure_Digital
Scroll down until you see the chart for "Speed Class Rating"
and just below that you can find a chart for "x-rating"
I don't know about your computer as I am not familiar with a MAC.
..
Movie clips from Digital Camera - Sony - Nex 3 - recorded on fine/wide. Uploaded to IPhoto on Mac 10.5.8 Dual 2 GHz PowerPC G5 - Memory: 10.5 GB DDR2 SDRAM

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