To play .DAV video files, you will need to use Smart Player, which is a video player similar to Windows Media Player or Quicktime.
Please click here to download the Smart Player software for PC.
Please click here to download the Smart Player software for Mac.
Once installed and you've run the Smart Player you will need to associate the .dav file format.
PLEASE NOTE: Make sure to copy the .DAV files over to your computer off of your external drive. It will not play directly from your external drive.