Try this if Kdenlive is having trouble with performance or seeking on your AVCHD footage.
DNxHD [1] is high quality, slightly lossy intermediate video format for HD only. You get near the quality of uncompressed, but with much reduced storage and bandwidth requirements compared to uncompressed.
Links:
[1] http://www.avid.com/DNxHD/
[2] http://kdenlive.org/rendering-profiles