I upgraded my sites to the version 4 player and it looked great. Quality was better and I liked the preload progress wheel. However after a week I noticed that there were lots of users viewing still frames instead of video even though the sound was playing. After testing on several of my sites I found that indeed about 1/4 of the time the visual would not begin to play unless a refresh was chosen. So I removed the player 4 and reinstalled version 3.x and the stalled video problem did not occur.
I have not tried to figure it out, but I wish it had worked.