I had created a Volume Adjust Extension for Alfred v1, now I've updated it as a Workflow for Alfred v2.
More info including a download link and the source is available on my website: http://victorquinn.com/development/#volumeadjust
But below are the commands it will accept for changing the system volume. Includes a notification of the exact numeric (0-100) volume level. There's a prettier and more readable table version on my website.
vol {number, 1-100} [invoked as “vol 30” or “vol 74”. Any number from 0-100 will work and the volume will be set to that percentage. So “vol 30” will set the output volume to 30%. Any number less than 0 will just set the volume to 0% and any number greater than 100 will just set it to 100%]
vol mute || vol off [Mutes the volume. Unfortunately, since Alfred just runs the Applescript and then terminates, it is not possible at this time to mute then unmute back to the same volume you were before the mute.]
vol quiet || vol soft || vol low [sets volume to 15%]
vol medium || vol mid || vol half [sets volume to 50%]
vol loud || vol high [sets volume to 85%]
vol up || vol more || vol + [invoked as either “vol up” or “vol up {number, 1-100}”. Used as just “vol up” it will increase the volume by 10%. But invoked as “vol up 30” it will increase the volume from its current level by 30%. So if your volume were at 10%, invoking “vol up 30” will end with the volume at 40%.]
vol down || vol less || vol - [invoked as either “vol down” or “vol down {number, 1-100}”. Used as just “vol down” it will decrease the volume by 10%. But invoked as “vol down 30” it will decrease the volume from its current level by 30%. So if your volume were at 73%, invoking “vol down 30” will end with the volume at 43%.]
