[MrQuincle]

Good point about it not being random over sequences. Would be fun to find a method that would obey more constraints and requires fewer flips than TH, HT from the other comment.

[Someone]

As https://news.ycombinator.com/item?id=25531532 said look up arithmetic coding (https://en.wikipedia.org/wiki/Arithmetic_coding)

It’s not 100% the same, but understanding it should enable you to use the same idea for this problem.