I have also had the no sound issue on some of my recording. I recorded the Grammies last night and was watching most of them on my replaytv. ReplayTv cut off the end of the show which kind of pissed me off, but it was a live event. I was recording it on MP and I know it recorded more than the replay. When I went into MP and clicked on my show... I had video but no audio. It played just fine with WMP. I told myself that I was going to work until I get this working... which I did.
After removing codec's and installing programs, I finally figured out why some of my shows did not have sounds. I guess some channels have AC3 audio and some do not. Seems kind of strange but that was the case. I could play some files just fine while others, it would not connect up to my audio codec. I installed AC3 1.11 and now it seems like every one of my recordings works.
I will keep testing, but I am very happy about this.... it was never fun to sit down and want to watch a show.... but then find out it how no sound.
I am just using a PVR500 card with analog cable. You can download that codec
HERE to see if it changes anything for you guys.