I think the only program you can edit poser key frames in is poser. Backdrop problem- if you have photoshop or something like then render your poser files at your size you want and then save it as a psd or tif so you can use the alpha channel in photoshop to layer the picture. In photoshop under select choose "load selction" and by defult usually it will show select alpha channel. Now you can copy or delete the empty area. I like this way so I have full contol of my seperate renders for other effects like camera blur and so on. Hope this helps.