If you are working in or Blender , "solid text" refers to text geometry that is a manifold (water-tight) object.

"Solid text" might refer to a specific or overlay used throughout the series. 2. 3D Modeling & Rendering

If 366mp4 is a specific file you found, it may be a compressed video from a niche archive or a surveillance system export.

Are you trying to text from a file named 366.mp4, or are you creating a 3D "solid text" element for a video?