How do I add new videos to a project?
You can't add new media to an existing transcribed project. Create a new project instead.
Once a project is transcribed, it is closed: you can't add additional media to it and you can't remove media from it. A key reason is that for post production, XML structure is critical and adding subsequent media to an existing project could corrupt the XML.
Instead create a new project and import the additional media to there. Then use folders to organize your projects.