Solution for those wishing do add a download button when using an RSS playlist. Thanks to James Herrieven for helping me solve this (http://dev.powered-by-haiku.co.uk/solutions/listy/): http://support.jwplayer.com/customer/portal/questions/11447158-download-plugin-with-rss-xml-playlists
This solution requires a path to an http video file (Apache/hls streaming folder, etc): 1. RSS playlist parameter: add a <jwplayer:downloadfile> parameter to each playlist item in the RSS playlist. For example, <jwplayer:downloadfile>http://pathtofile/download.mov</jwplayer:downloadfile>
2. Add a download button to get the file specified in the downloadfile paramter: <script> jwplayer().addButton( "images/download.png", "Download Video", function() { window.location.href = jwplayer().getPlaylistItem()['downloadfile']; }, "download" ); </script>
Safari: the file opens in a new window. The user can then save the file by going to File > Save As (Format > Page source option).
Chrome: file automatically starts downloading.
Many thanks to James Herrieven for helping me figure this out.