I think what you need is to set
EDIT
$('#jw_container').show(0,'', function() {
// Animation complete.
jwplayer().load("https://content.bitsontherun.com/jw6/" + key + ".xml");
jwplayer().play(true);
});
Hypothetically it might be that the playlist is not loaded so the play method is being executed on nothing. So this might also work:
function playTrailer(key) {
$('#jw_container').show(); // show video player
jwplayer().load("https://content.bitsontherun.com/jw6/" + key + ".xml");
jwplayer().onPlaylist( function(event){
jwplayer().play(true);
});
}