use

We use the past perfect progressive to talk about longer actions or situations which had continued up to the past moment that we are thinking about, or shortly before it.

• The President had been speaking for about half an hour when trouble started.
• When I found Ann, I could see that she had been crying.
• I had been reading the novel for hours when the lights suddenly went out.

past perfect and past perfect progressive: differences

The perfect progressive tenses are often used to talk about more temporary actions and situations; when we talk about longer-standing or permanent situations we prefer perfect tenses.

• My legs were stiff because I had been standing still for a long time.
• They lived in a castle which had stood on a hill above the village for 1000 years.