Back in the day when online learning was channels on Community Antenna TeleVision systems reserved for Community Colleges, I was studying the digital bandwidth required for online learning via telecommunications.
Although I don't have a reference, I found a study by a German university that compared classes delivered by television with classes delivered with a combination of sound, pictures, graphics and text.
The result was that the latter was as effective as video for all categories of classes, even those teaching kinetic skills such as golf and tennis.
Moving pictures, especially those of the head and shoulders of a professor delivering a lecture, are completely unnecessary.
I think that the key to online learning is the care and expertise with which the content is developed, especially the narrative, pictures, graphics, and reference material, as well as the design and effective use of collaboration tools by the TAs and students.