I just built a nice computer for video editing. 16gb ram, SSD, and a Intel Xeon E3-1230 V2 3.3GHz Quad-Core Processor. I am unable to render with multiple cores though. In Settings>Configure KDEnlive>Environment If I change the processing threads to anything higher than 1 my effects mess up. Every time I have a sped up clip (does not matter what speed as long as it is higher than 100%) the last few frames will freeze. Also, the highest the "processing threads" menu will allow is 3. Is that supposed to be that way? This is very disapointing considering this computer build was supposed to reduce rendering time by a lot. My CPU monitor is showing 8 cores and only one maxed out. Any ideas?

I see under Proxy Clips, the ability to enter a number of Concurrent Threads - mine says 2
Further down udner the MLT Environment tab, is the ability to enter a number of Processing Threads. This says 1 for me.

But when I render, I select a number > 1 for encoder Threads (on render panel). Just for this exercise I have selected 4 and I can see multiple cores hammering away (have an 8 core cpu: 7 3770).
By chance I happened to have a speed effect, and I didn't notice any issues.

Hope that helps.