English Grammar - Verbs - Past Perfect Continuous

FORM Past Perfect Continuoussubject + HAD BEEN + VERB+ing
Usage:
The past perfect continuous tense is used to talk about longer situations that continued up to the moment in the past we are talking about.

Examples:
By the time I left France we had been living in Paris for twelve years

It is also used to say how long something went on for up to a past time.
Examples:
I apologized because I had kept them waiting for 5 hours.
Using the Past Perfect Continuous before another action in the past is a good way to show cause and effect.Examples:We were tired because we had been playing tennis during 6 hours