No, no codec problem. It sounds like there was a corruption withing the audio stream and when you trying to extract and merge the audio stream, it mearly got rid of anything after the corruption. Not sure if there is too many ways to fix this. Might try using TMPGEnc's demuxer and getting the audio stream and sending it through besweet or some other special audio encoder. I don't know much about audio, but that's an idea. Then again, it may do the same thing with the audio when you demux. Then you should try using VirtualDub and extracting to wav. *shrug*