When I try to add a poster:
[video mp4="vid.mp4" preload="true" poster="pic.jpg" width="940" height="480"]
it insists on putting the Oceans picture.
I opened the file video-js-wp.php in line 61, there was
$flow_player_poster = '"http://video-js.zencoder.com/oceans-clip.png", ';
changed it to
$flow_player_poster = '"'.$poster.'", ';
and it works fine now.
justed wanted others to know.