In app/assets directory create a folder named as "jwplayer" and put jwplayer.flash.swf in it. So that the directory structure looks like app/assets/jwplayer/jwplayer.flash.swf. And also update the browser to latest version otherwise it will not support HTML5.
If it will still throw the same error then keep the changes as it is and replace the line
flashplayer: "<%=asset_path('jwplayer.flash.swf')%>" with
flashplayer: "<%=asset_path('jwplayer/jwplayer.flash.swf')%>"