As a professor, I don't think exclusive online teaching is long term viable for university students let alone school children. But a pre-recorded lecture is us

As a professor, I don't think exclusive online teaching is long term viable for university students let alone school children. But a pre-recorded lecture is usually much shorter than a live lecture. The one-way communication of a one hour class can usually be condensed into a 10-20 min video recording. This is by using a script that optimizes the time to communicate the information in the best possible way. The rest of the time should be spent learning by doing or talking to others.