I've seen some 10-30min clips on youtube from them, so there might be previews if you hunt the clips down on their channel.
I've caught a few live shows or the rebroadcast, kind of hit or miss. If you can't catch it live, I think the trick is to find a photographer who's work you respect try and find a clip of them teaching something, then make a decision. If you follow them on facebook or other social media you'll improve your odds of remembering when someone you want to see is on.
If you're looking for classes online, also check out the Kelby videos.
If you're hunting for free ones, then B&H Seminars are freaking awesome (and having seen their Oct schedule, I suspect I'll be watching a lot of video in Nov.), and given the forum this is in it's worth mentioning, they did do an entire wedding shoot. Many of the Adorama videos are quite basic for me (sort of a broad sampling bot not too in depth), but I think I've scouted out every deconstructing video Joe McNally's done.