Tips to get flacs to show up in db?

I am trying to figure out a universal format that LMS and my media players will support. Some mp's won't play, no mp4's will play so I thinking about flac

I just made my first conversion to flac as a test but it doesn't show up in lms after doing a rescan. The extension is .flac What does it need to be so lms can see it?

And do you think flac is the best universal format to use?

Thanks.