I of course here make the assumption that it is fairly easy to ascertain whether we are watching/hearing “vernacular” singing by itinerant professionals (true entertainment) or whether we are the presence of self-expressive, lyrical balladeers who sang because of sorrow, frustrated love, and the like, and in a non-operatic mode: that is, in a not-for-audiencing style (neighbors and sisterly circles excepted) wherein verses were always in flux, and mood and circumstances dictated by predictable tragedy.
The variable that helps draw a boundary is I think humor. Clowning and gesturing in a comic mode (slapstick), or impersonating animal sounds (old Macdonald has a firm….) or virtuoso class patter-song. (British Music Hall) are the domain of workers-of-the-crowd; no clowning or wit, no one pays. Performers with sad feelings to sing “out” do not laugh, least of all at their own expense. Crying and pointing fingers, raging, and the like can carry them past misery, but this too is (in N. Chinese context, where parents are the most common cause of sorrow, but must not be offended publically): screaming at (or rather “about”) the middleman (-ess) is the only way to manage things. (rather as the GPCR was faulted by complaint against Jiang Qing, never against the real problem-maker, Chairman Mao).
To this of course we must of courdr append the tumbling/acrobatics stunt-man(-men), but they are still (like humorists) “relief”: entertainers, usually young, with no regular venue, inheritors of “schools”, whence of course the current foreign fascination with THEIR kickboxing, which is now a part of both our and their “break” cultures.
Point is: in China films that are best remembered for internal storytelling, the vernacular minstrel(iste) is both logical and inevitable as the subject, the (indirect) narrator, the makers of the window through which stories about story-telling are seen.
This overlay of costume and role is very germane to Zhang Yimou’s debut film Red Sorghum. Because the character who walks us through the tale (his name is Yu Zhan’ao in the novel) is of this class of minstrel-toughs. And because so also is his singing. If it sounds “performed”, that’s because it is: we never in this film confront “private” or truly amateur performance in any variety. If his bravado seems theatrical, that too is because he was of the performing underclass. And if he winds up unwisely picking a fight with the Japanese road-building contingent, and getting fellow workers and wife killed off in a 2-minute gunfight, that too comes from role-playing gotten of hand. (The earlier confrontation in the tavern with a much stronger hoodlum+bodyguards predicts this).