Not sure what you mean by uploading a video on Camtasia. Do you mean you have recorded your own video and it is not showing up in the Clip Bib or you are trying to Import a video into Camtasia ? What version of Camtasia are you using and please provide more information if you can of where you are trying to upload to for example YouTube, Website, Etc.
Thanks for posting and the more information provided the easier it will be to help you. Have a great day/night.