Quote - To the OP :
if you already  have a satisfactory run/walk in place animation you can move him forward literally with TWO KEYFRAMES one at frame one and one at the last frame
the Value at the last from with LINEAR INTERPOLATION will determine how fast he moves forward

Like HERE:

if you are not experienced with the graph editor then please start HERE

first.

Cheers

There wasn't any sound on the first one but I enjoyed the second one immensely. Thanks Wolf.