As part of the Map Maker's Toolbox project I've found a way to have motion tweening within Minecraft.  
It supports multiple kinds of the same mob (each one dropping a different kind of loot), chances, different stack sizes of the same item, etc.  

To use it,  open the schematic in MCEdit and place it anywhere in your world. Then use command blocks to create the animation specifically for your door:

So, if you're creating maps and would like to have smooth animations in them, you can download the basic setup here.  
(In the video I refer to my Github repository which is an alternative place to download the schematics from.)  

A few important things:  

• Does NOT need to be inside the spawn chunks to work.  
  
• Can be placed multiple times in one world and work as intended. 
  
• Gamerules needed to make this work as intended are: commandBlockOutput set to false.
  
• You need to keep at least 1.5 blocks of distance above the animation for it to animate correctly.
  

Feel free to use this anywhere; there is no need to credit me unless you're doing something that focuses around the contraption itself such as creating a video about it.