We do not have a built-in capability to use different images for the poster image and a thumbnail, but if you make a custom listbar via Javascript and CSS, you can define a different image URL to use as your thumbnail. Here’s a code example:
<script type='text/javascript'>
jwplayer('demo').setup({
playlist: [{
file: "bunny.mp4",
image: "bunny.jpg",
title: "Big Buck Bunny trailer",
thumbnail: 'bunny-thumb.jpg',
description: "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc sagittis velit non leo porta laoreet. Donec blandit tincidunt placerat. Curabitur commodo erat sit amet sem elementum aliquam."
},{
file: "sintel.mp4",
image: "sintel.jpg",
title: "Sintel trailer",
thumbnail: 'sintel-thumb.jpg',
description: "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc sagittis velit non leo porta laoreet. Donec blandit tincidunt placerat. Curabitur commodo erat sit amet sem elementum aliquam."
},{
file: "tears.mp4",
image: "tears.jpg",
thumbnail: 'tears-thumb.jpg',
title: "Tears of Steel trailer",
description: "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc sagittis velit non leo porta laoreet. Donec blandit tincidunt placerat. Curabitur commodo erat sit amet sem elementum aliquam."
}],
width: '480',
height: '270',
skin: 'skins/glow/glow-edited.xml',
});
jwplayer().onReady(function(){
var myVideos = jwplayer().getPlaylist();
for (var i = 0; i < myVideos.length; i++) {
//put the code to get your rating here
document.getElementById('listbar').innerHTML += '<div class=listbar_item onClick="jwplayer().playlistItem(' + i + ');"><img style="float: left; height: 60px; margin-right: 5px;" src=' + myVideos[i].thumbnail + '><b>' + myVideos[i].title + '</b><br>' + myVideos[i].description + '</div>';
}
});
</script>