Thank you Don for getting back to me. I really love these forums and how helpful people are
The problem turned out to be the createInterpolant function was not being stringified, so when I over-wrote the “tracks” part, the function was lost.
I got it working somewhat, by iterating through the animation, and just replacing the times and values. But found my approach is fraught with all kinds of other perils. I think what I need to do is write a function to re-target, so I can use the normal BVH loader, and it will match the bones in the BVH to the ones in the Makehuman skeleton. I spent about 10 hours trying to avoid 3 or 4 hours of work. lol