Hi, I'm new to a mac and a lot of the whole video/audio encoding/editing world. I realized that a lot of the problems I googled led me to these forums so this would be a good place to sign up and ask away. So, I'm getting very frustrated converting some of my matroska videos to an mp4 container format (to put into itunes). For certain videos, the video is fine, but I seem to be missing half my audio, as if it was lagging/skipping for the entire duration. Under source it says the audio is "Unknown (VORBIS)", which leads me to my first question: What's an easy way to see what type of video and audio you have? I'm assuming my audio is ac3 since the mkv files I have problems with said how I may need an additional codec to play the audio. Strangely, some of the files that give me the message I am able to convert without problems. Currently I have ffmpegX, MPEGstreamclip, and VLC Player, on OS X. VLC Players gives me an even greater slew of problems in converting the mkv-- either I only get audio, or the video is all small blurry as if it was only a couple pixels. I know there are other programs like MP4box, MKVextract, and VisualHub, but I really don't want to add any more programs and make things more complicated if I don't have to. I've tried changing the sample rates if that means anything and I still have the same problem. Also, why can't I choose AC3 Passthru as the codec? Does that mean that the source audio really isn't AC3? Thank you mac experts!