Definition:     The Perfect Progressive tenses are used to express the time that has elapsed between two points in time.  The Future Perfect Progressive verb tense is used to express the time that has elapsed between the beginning of a continuous action which is before, at, or after the present time, and a point in time in the future.

Example:   When you will call me tomorrow at 9:00(point in time), I will have been watching the movie for 30 minutes. I will start watching the movie at 8:30 and will watch it continuously until you call me at 9:00.  To express the time elapsed between these two points in time we use the following sentence:

                     When you will call me tomorrow at 9:00, I will have been watching the movie for 30 minutes.

How to write the Future Perfect Progressive:

To write the Future Perfect Progressive you must use the future of the verb To Have, the Past Participle of the verb To Be, and the –ing form of the verb you are conjugating.