Changng volume of video?!

Hi i am currently looking for a way to incrementally change the volume of a movie clip that i have on the stage. I have tried:

[AS]ns.soundTransform.volume = ns.soundTransform.volume - 0.1;[/AS]

but as i am new to modifying video within AS3 i cant figure it ut. i know how to change the volume to a set level but i have buttons on my vid player for volume and i want the volume to go down by 0.1 and up by 0.1 when those buttons are clicked can any 1 help me? thanks