melt / mlt rendering speed issue

Hi, I began to use kdenlive since only 2010.

Any one knows weather melt / mlt is a software only rendering or can it use GPU on graphics accelerators? How to config?

I found large HD rendering slower then expected, and gets bugs with I guess some codecs. In particular when melt / mlt render my large jobs 1920x1080 system resource meter says my 6 core CPUs are only running between 45%-68%. When only I started off 2 rendering jobs it goes above 90% CPU usage.

When there are many video layers and effects, a hour of video could run into 2-3 days of rendering.

When rending to e.g. flash some layer (foreground) of video (MTS file format) will render at extra fast playback speed (their video about twice speed of their own audio from that same file) & then freeze up at some stage while the background (flv or mpg formats) & audio runs normally. This problem reduced or vanished when I render to smaller frame sizes.

I tried to use nice / renice command to push rendering speed of melt / mlt without finding much help.