If instead you were to use the NewVideoPlayer (http://forums.roku.com/viewtopic.php?f=34&t=91672&p=516080), which you can get from https://github.com/belltown/Roku-NewVideoPlayer
if item.StreamFormat = "" then 'set default streamFormat to mp4 if doesn't exist in xml
item.StreamFormat = "HLS"
If item.StreamFormat="hls" then
<item sdImg="pkg:/images/Tsc214x144Sd.png" hdImg="pkg:/images/Tsc290x218Hd.png">
Where and which file can I modify to add this code in? The 'authentication code' is generated elsewhere so I cannot add it directly to the feed XMl file beforehand. Like for example, the XML is read and if the title has HD in it, then streamUrl = streamUrl + authentication code
stream.url = _getXmlString (media, "streamUrl")
stream.url = stream.url + authenticationCode