Seamles looped animation from a Motion Capture?


I wanted to ask how to make a seamles looped animation from a motion capture bvh file within Blender?

In BVHacker I can mark the start and the end of the loop, then cut it and make it automatically seamless. But I do want to be able to do that within Blender. I had a look at the graph- & nla editor and I tried to google it but I have only found the cycle-modifier and that is not what I am looking for. My End frame is a bit different then my start frame. It needs to be interpolated. There must be a more or less easy way to create a seamless loop in Blender?

Can someone explain to me how or point me to a guide on to how do so?