Are there any guidelines for positioning of sound buttons (play, pause, mute)?
I'm not sure what the standard is for this, but when I'm annoyed by sound I always look in the upper left, then right-hand corners for a mute button.
Failing that, I look for a settings area.
You should also consider where you have put other user controls, and whether or not it makes contextual sense to group this with them.
Play and pause should toggle
Volume control should be separate from mute (dragging the volume down is not clear on how to stop the sound)
Play button should be in close proximity to the timeline.
UI design should blend into the background of what is being viewed.
Small, but big enough click area for users to miss with their selecting device.