That may explain it. When I Googled DAV files, NCH Prism came up at the top of the list and I noted that many other converters did support DAV so I might have made a bad assumption that Prism is capable. Still however, some of those others have a limitation on the length of DAV that can be converted using their trial versions, so that led me to wonder if the paid version of Prism would work (the length of the clip I'm trying to convert is longer than 5 minutes). Prism does open the DAV file and display the first frame. The converted mp4 file is also about the right size but has the padlock icon on it, so still wondering. Thanks for the response.