As long as our player has been around, we have received requests from our customers asking to slow down video playback. Unfortunately, Flash never exposed any sort of playback speed control across the board. Take a video with progressive download -- by default controlling playback speed is not supported. The only way for this to work is by using RTMP, with either Adobe Flash Media server or Wowza Media Server (FLV only).
As a support team, we would get around this by using the player API to mute the audio track and essentially make the play pause very quickly, over and over again, using a timer, to simulate the illusion of slow motion, however, this solution was not very elegant, and it made the play icon flicker.