Failed to save changes while editing video, why?

After you edited video by clicking Edit->Video Edit or Edit->Trim, don't forget to click the OK button to save the changes.

You change will take effect only by converting to a video files. To do so, go to Profile list at bottom to choose an output format, and click the Convert button to create a new video file with your changes. When complete, click the Open Output button to play the video you've edited.