A quality brush motor would be used as the motion to electrical power converter.  Perhaps a 24v motor with an efficient 50:1 speed reduction gear attached would be a place to start.  The shaft of the speed reduction gear would be connected to a long arm, with a weight attached.  The length of the pendulum arm and the mass of the weight might have to be fine tuned to maximize the swinging motion. In another concept, the pendulum shaft is attached to a spring to extract energy from the up and down motion.  

The idea is that the up and down, as well as side to side motion, of the walking human gate would cause the pendulum to swing maybe 30 degrees in each direction.  The high gear ratio would turn that 1/12 of one full revolution into several full rotations of the DC motor.  The positive and negative voltage from the brush motor, acting as a generator, would be rectified and converted into a fixed polarity voltage using a rectifier.  A 500ms swing half cycle, converted to say 4 complete rotations would be the equivalent to 4/0.5s x 60 = 480 RPM.  This speed might be about one tenth that of a 24v motor, so the peak voltage would only be 2.4v or about 5v peak to peak. Assuming a perfect rectifier, the system might be able to crank out a 5 volts DC.  I’m not sure how much power could be extracted but I believe that this system would be much more efficient than a bouncing magnet approach.  If someone does build up such a device, please let me know how it works.