If it's progressive playback then you can only seek to keyframes. If you set keyframe distance at 10 seconds (standard for some media) and skip 10 seconds it will find the next keyframe AFTER the 10 second mark you specify. Worst case scenerio in that situation is you'll skip 19 seconds.
You don't need to assign a variable to it, you can just:
aud01.playheadTime += 20;
It means you have not hired a host who has a streaming server to serve your videos from over a streaming protocol.
Basically progressive play is when you load any http:// address pointing toward a file and it plays off a website. Progressive means you cannot skip to any part of the video that has not downloaded. You can only progressively play it as it downloads.
Alternatively, on a streaming (non-progressive) server you can skip at any time to another part of the movie regardless of keyframes.