We might write 'Have been waiting for you.' as a note, or send it as a brief text message. In 'note form' style of writing, it's common to miss out the pronoun, especially if it's clear that the subject is 'I'. However, native speakers don't miss out the personal pronoun when speaking. We contract the 'I' and the 'have' to 'I've', and, in many accents, this sounds a little like 'av'. What we are saying is 'I've been waiting..'. What you are hearing is ' "Av" been waiting'. But that '"Av" sounds is NOT 'have' - it's actually 'I've'. The pronoun is there. I hope that clears up your confusion.

At times people will omit the personal subject pronoun. I do not recommend doing this. The proper way to say it is " I've been waiting for you". More often you will hear non-native speakers or lazy natives omit the personal pronoun. You will sound more educated and be better understood if you just include it.