Время Past Perfect Continuous указывает на действие, которое началось в прошлом, продолжалось в течение некоторого времени и либо закончилось непосредственно перед неким моментом в прошлом или все еще не закончилось к некоему моменту в прошлом.
I had been typing this text for 2 hours and then found it on the Internet.
Я набирал этот текст два часа, а потом нашел его в Интернете.
I had been waiting for his airplane for 2 hours when it was announced about delay.
Я ждал его самолет уже два часа, когда объявили об его задержке.
Образование Past Perfect Continuous
Утвердительные предложения:
I had been playingWe had been playing
You had been playingYou had been playing
He / she / it had been playingThey had been playing
Вопросительные предложения:
Had I been playing?Had we been playing?
Had you been playing?Had you been playing?
Had he / she / been playing?Had they been playing?
Отрицательные предложения:
I had not been playingWe had not been playing
You had not been playingYou had not been playing
He / she / it had not been playingThey had not been playing
Для того, чтобы поставить глагол в форму времени Past Perfect Continuous, требуется вспомогательный глагол to be во времени Past Perfect и причастие настоящего времени (форма V-ing) смыслового глагола.