Making game object transparent?

I have a movie clip with a transparent background I want to map onto a plain so in the game all you see is the clip playing. I've tried using a standard shader with the rendering mode set to transparent but it doesn't seem to work(you can still see the edges of the plain). I've also tried using a glass shader but that refracts the light so you get strange results. Anyone got any idea's I've search the forums and anything I try doesn't work. (I'm using Unity 5.4.3)