Hello,
I'm software engineer with master's degree in IT, my specialization is intelligent systems. My bachelor's and master's thesis were about developing smart Android apps. For my master's thesis I worked on the implementation of algorithms of detection specific objects (cars) in camera view a measuring the distance to that objects by using only the laws of perspective. I have made an Android app do show GUI of possible useful application for drivers that looking for safe distance from following cars in traffic. Unfortunately, performance of modern smartphones is not enough to do it in real time.
Now to your problem, I'm not sure I understand it, Android API not allowed to approach to video frame by frame. So, in my opinion, it is not possible to calculate exact time interval between frames be cause you just can't identify them. I could say more only after I get your problem more specified to understand it completely. Please, contact me and we will discuss it, also I can send you examples of my work I mentioned above (something I have on my portfolio but videos didn't work in some reason).
Looking forward working together.
Thank you.
Best regards,
Andrej Henry
P.S. Mohli bychom si povídat i český, pokud tedy umíte :)