Nova77 and I had an ongoing conversation recently about how CorePlayer struggles with AC3 audio after I discovered that installing Perian fixed this issue about 90%. As a big user of VLC and Mplayer for about a decade before I bought CP in Jan. I hardly ever use Quicktime for playback so in turn I never bothered installing Perian as I didn't need extra codecs for it. It turns out that Perian makes some codecs truly system wide for any compatible app. Most of the MKV wrapped h.264 I play has AC3 audio so this is a huge help! I still have some issues with XviD that has AC3 but all the h.264 that had it play fine now. Just something I wanted to share with the few CorePlayer users out there. Both Nova77 and I are running version 1.3.6 of CorePlayer and OS X 10.5 Leopard for the record. Perian can be found here for those that don't have it or know of it.