I'm looking for any references that exist for what a good video length for an online math class should be.
I am aware of these three papers but these are basically only for MOOCs - I'm looking for something in a mathematics class that's required - Ideally measuring long term learning but at this point anything is welcomed.
Effective educational videos By Cynthia J. Brame, CFT https://www.lifescied.org/doi/10.1187/cbe.16-03-0125
How Video Production Affects Student Engagement:An Empirical Study of MOOC Video - Guo et al., 2014 http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.714.195&rep=rep1&type=pdf
Understanding In-Video Dropouts and Interaction Peaks inOnline Lecture Videos
EDIT: I'm looking at the university [undergrad particularly] level. Yes I agree that static videos usually aren't best for learning (but say for algorithm demonstration; I find a video to be vastly more effective and efficient than a long prose describing the algorithm as both a learner and as an educator).