Hi @TomCheung679, thank you for asking about this! To allow for better mobile learning, students can always download course videos within the Udemy app for offline viewing, as the video content in this case is encrypted. When students download video lectures in the Udemy mobile app, they are saved as encrypted UFO files - these files can only be opened in the Udemy mobile app.
Due to piracy concerns, course videos are not available to students for download on a computer. As the instructor, you can choose to enable or disable this setting. For more information, check out this support article
We understand how valuable your content is and we are committed to helping you protect it. For more information on how Udemy protects your content, please click here.