How do I play logitech videos?

The files are all .avi and I thought they should play on QuickTime Player. Instead I get the message, "The document "Video 17.avi" could not be opened. The movie is not in a format that QuickTime Player understands. You may need to install additional software to open this type of file." When I click on tell me more, it lists AVI files as compatible with QuickTime Player = unhelpful! What now?