When I try to upload video to Camtasia, I get error message cannot load file no decoder was available for the following codec: xvid
The video FORMAT I am trying to upload is avi, I even converted it to, FLV and still got same error message. I am running windows XP on my PC.
I even downloaded video codec from Camtasia and did not help. I am using 30 day free trial for SOFTWARE. Windows Media Player, WMP, is the problem.
Thee are many free video converters. One oldie is Format Factory
http://www.pcfreetime.com/

The Windows Media Player will refuse AVI formats that it can not understand. Use an alternative media player. One is VLC. (Video LAN)
http://www.videolan.org/index.html

No need to THINK it is just your computer. WMP disappoints many users.
http://wiki.answers.com/Q/Windows_media_player_11_refuses_to_play_your_avi_holiday_movies

Just try another media player. Even the Apple Quick Time for Windows.
http://www.apple.com/quicktime/what-is/
Maybe the OP is IMPORTING the video with Xvid codec needed...
Quote

When I try to upload video to Camtasia, I get error message cannot load file no decoder was available for the following codec: xvid

See title : Unableto import video to camtasia

Maybe the OP is importing the video with Xvid codec needed...http://techsmith.custhelp.com/app/answers/detail/a_id/3036/~/camtasia-studio%3A-unable-to-decode-video-stream