Put in layman terms - your best possible entropy is a case where every allowed character appears with roughly the same chance (i.e. there is no super common or super rare characters). The most extreme low entropy case is where only one character appears all the time so the password is completely predictable if you know how long it is.
I would recommend you run two tests. One with the same video over and over video and one with 5 or so videos filmed under similar conditions to measure how much of the randomness actually comes from different videos vs. your algorithm. For your videos genererate 100k+ passwords and count the number of times each character appears to get the probability of each character. Then use what you learned about Shannon Entropy (using the probability of each letter) to determine how much entropy your passwords have.
