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Vanos controls cam timing, as far as WHEN valves open during the rotation of the engine. Vanos can adjust the cam to open sooner or later as needed. I don't believe that Vanos will adjust cam duration, only timing.
Valvetronic controls valve lift of only the intake valves, acting as the throttle valve, and minmizing pumping losses, since air under less vacuum is more readily available right at the valve instead of at the throttle valve.
Neither of these two things control cam duration.
The wave of the future is solenoid actuated valves, no cam at all. There will be solenoids on every valve, and they will open when, as much, and for as long as is necessary to acheive max performance and efficiency for the current throttle demand.
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