I used Camtasia to create some video training modules for a client, but she said she couldn't see the video portion. She could only hear my audio. She was using Windows Media Player. I asked my assistant to view the avi files on his computer. He used Windows Media Player. He couldn't see the visuals either.
Then he opened free open-source VLC Media Player--and everything ran perfectly. I loaded VLC on my client's computer, and all runs smoothly.
I would recommend VLC Media Player.