Title or Poster image with s2stream tag?

[s2Stream player="jwplayer-v6-rtmp" player_path="/jwplayer/jwplayer.js" 
file_download=""/URL-Path/video-file.mp4" player_width="640" 
player_height="380" player_image="/URL-Path/title-image.jpg" 
download_key="universal" check_user="no" /]

If I want to show a poster image when a video page is loaded, instead of a ‘black’ video box, how would I call the image ?

According to the language this sub-tag syntax should work --> player_image="/URL-Path/title-image.jpg"

Anyone care to clarify ???