I have the same problem, it started about 2 or maybe 3 weeks ago, everything was working flawlessly before that, I started playing in November and never had a problem before then. I'm certain it is a bug with this game, because I play lots of other games and sound works flawlessly with them, I can even listen to music and watch stuff without any issues when the sound dies in ff14, the only solution is to restart the game, I don't have any crackling or stuttering as other people are reporting, when the sound works it is absolutely flawless. It seems to occurs mostly in dungeons, when I am questing and exploring it can be hours/days between it occurring, I just did a dungeon, and not 5mins after starting it my sound dies, so I restart the game again and a couple of mins alter the sound dies again.

I really hope this will get fixed soon, it is really tarnishing an other wise near flawless game!