Peking Opera has a distinct pronunciation, that is at first similar to Mandarin, but to astute listeners, certain characters appear to have alternate or even non-Mandarin pronunciations.
尊一声过往宾朋听从头 (shen, pong, tin)
一不是响马并贼寇 (bin, ze)
实难舍街坊四邻与我的好朋友 (jiai, pong)
As you can see, the differences in pronunciation seem consistent, as if it is a formal part of Peking Opera instead of embellishments by the singers.
So is this true - there is a formal set of pronunciation rules for Peking Opera, analogous to a dialect? Where did this come from, was it based on one or many dialects, and if so which ones?