When you add movie to the contents, use embedded object menu of the WYSIWYG editor.
Select the position to put the embedded object in the content area of WYSIWYG editor, and click icon. Then input pane appears.
Input the code of the embedded object, and push "Submit Query" button. Then the Embedded Object is added to the content area.
Select the embedded object to edit in the content area, then the icon is activated. Push the icon, and show input pane to edit the embedded code.
Edit the embedded code, and push "Submit Query" button.