You may set the number of key-frames that you would like in your animation and the length of the animation by indicating how many key-frames are rendered per second.
An animation may be closed or open. An open animation stops when it reaches the last key-frame. A closed animation will run continuously. Note that with closed animations, the first key position must equal the last key position in order to achieve smooth animation. When you choose "closed", the last key is automatically set to equal the first key, and cannot be modified.