I have found a video where BBC explains how to pronounce "have" when this verb is used as an auxiliary. When it comes after a consonant sound, it's pronounced /Əv/. For example: "I would have been late" becomes "I'd've been late".  

If my alarm hadn't gone off this morning, I'd've been late.

Non-conditional examples: 

Your parcel should've been delivered yesterday.

I would've done it differently.

We might've made a mistake.

The police've arrived. 

Personally I still find it difficult to pronounce it that way...  anyway, keep practicing.

Source: https://www.youtube.com/watch?v=z7Ya1BFLRmg&list