The Mac has iTunes control keys on the top row of the keyboard. You don't need to have iTunes as the front app to use them.
F7 - Go to the beginning of the current track. If you are already at the beginning of the track, you are taken to the previous track.
F8 - Toggles between Play and Pause.
F9 - Go to the next track.
You can also adjust the volume from the keyboard.
F10 - Toggles Mute on and off.
F11 - Decreases the Volume.
F12 - Increases the Volume.
If you have an older Mac keyboard, you might not have iTunes playback controls, but you will have the volume controls. The volume controls appear in different places on the top row of keys depending on the keyboard, but have the same key markings as on the current keyboard.
The iTunes Rewind, Play/Pause, and Fast Forward only work in iTunes. For whatever reason, they don't control playback in iMovie, YouTube or any other app that I found.
The volume keys work always work to adjust the volume.
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