Start up animation for running

So the title may be confusing, but basically I want an animation to play when you start walking for about a second, and then the animation changes to normal walking cycle. How would I script this? I normally get pretty confused when walk cycles/idles are involved so I use a basic animation handler from the toolbox, but this has no function to create this effect.
I dont want the script, I just need a general idea.

Im doing this so I can create a smooth transition from the idle animation to the walk.