I have Vista HP. I have a DVD on which I've already burned a number of FLAC rips from CDs. The DVD must have been formatted in the process. I'm now trying to add one more such file. I'm being asked again to choose live file or mastered format. I thought I had chosen the former when I burned all the files now on it, though I can't be sure. When I try to choose it again it says it will format the disc and I will lose all existing files. How can I tell how the disc is currently formatted, and why would it need to be done again? Any other suggestions would be appreciated.

In windows explorer, right click on your cd drive and click properties, see what is next to File System