8. Define the Video Source Machine Name Field
Once on the Add Field screen:
Add a New Field select field = Text (plain).
Re-use an Existing Field select field = leave as is.
Label field = Video Source Machine Name.
Machine-readable Name field = this will auto construct from the Label field - it's suggested that this be overridden to include the same naming convention started with the other field that's present in this media type - media_video_source_m_name. (There is a limit to the number of characters that can be used.)
Click the Save and Continue button.