How do you start and end a motion graphic background with the same frame?

It would probably be easier to just re-create the blobby stuff with Fractal Noise, Turbulent Displace, massive blurs and a coloring effect like Colorama and then create a clip of whatever length is needed. Other than that the simple trick to making stuff loop seamlessly is to place two duplicate layers on the timeline aand overlap them in the middle, create an "invisible" cut or cross fade and then trim the comp so that start and end show the same frame of the clip. the rest we can't know. The length of the clips and number of baked in loops would be determined by whatever playback method you use. You would want it to be long enough so the short jump/ freeze when the clip rewinds doesn't occur too often, but you also wouldn't want it to be infinitely long to not have to deal with hunky clips, long render times and potential technical issues on the playback device.

Mylenium