Ever since I installed lion I've been having this problem where the sound on apps like quicktime, dvd player, safari, itunes and other apps that play video and audio would stop working all of a sudden after a period of time. Once this happens video wouldn't play and neither will audio in itunes or on youtube. The only way to fix it is to restart. Is there anyone else having this problem? I upgraded directly from snow leopard and never had this problem before.