Media Server :: Dynamic Video Shifting?

I'm creating a custom video player where the user can select to play the same video at different speeds (100%, 75%, and 50%).We have rendered 3 different MP4 files,one for each speed, and then there is a mechanism in the video player to load each video as the user demands it.It works fine so far, except that when a new video loads,it begins to play from the beginning, not at the point where the previous video left off (which is crucial).

I thought it would be as simple as using either ns.play("videoname", videotime) or using a ns.seek(videotime), but in ether case,the new video still will only play from the beginning.Here is the code, which includes some calculation for adjust the time depending on the shift from 100%, 75%, and 50%.

function switchSpeedVideo() {
var currentTime:Number = ns.time;
output.text = currentTime.toString(); // outputs correctly[code].....

What is missing here?Currently, I am using HTTP connection("HTTP Pseudo Streaming" with Wowza on SimpleCDN).Does this require RTMP?