The Weekend's Viewing: Louis Theroux: Twilight of the Porn Stars, Sun, BBC2 A Ventriloquist's Story: Her Master's Voice, Sun, BBC4

I suppose if you are going to describe a fresh face in the world of porn "rising star" will do as well as anything.

“Coming talent” might serve as well, of course, but it's a touch gamey, even if Louis Theroux: Twilight of the Porn Stars went out well after the watershed. While “rising star” was an apt description in one regard, though, in another respect it didn't make any sense at all. Xander Corbis may be in demand right now for the reliability of his performances, but he's in an industry with terminal droop, one undone not by Aids (which hung over the business when Theroux made his first film about porn in 1997) but by the viral threat of the video upload. That was Theroux's rationale for going back now – to look at how porn has been irretrievably changed by amateur exhibitionism.

He was also going back, I suspect, because he knows that the porn trade will reliably deliver jaw-dropping moments. The armature for his film might have been an anxiety about the psychological effect of the business on those who work within it, but this was a classic cake-and-eat-it deal. In one and the same sequence you can question a young woman about how her private relationships are affected by having sex with strangers and also summon the mental picture of her lying back while five men ejaculate over her face. As it happened, this commission had caused a little bit of friction between Cagney and her current partner, Monté. He wasn't sure she should agree to it. She felt that he wasn't thinking of her career: "I know that that's the kind of scene that might possibly win me an award," she said in exasperated tones.

Theroux is never judgemental with the people he talks to, but this wasn't a flattering portrait of the trade. Do you ever warn girls about the psychological downsides of porn, he asked a female agent. No, she replied scornfully, "because then I would talk three-quarters of the girls out of the business and then we wouldn't be in business". Another of his subjects, Rob Black, a shock-porn producer who'd spent time in prison since Theroux's last visit, reminded you of Al Pacino in one of his grubbier roles, a jittering moral vacuum just this side of psychosis. And Theroux had no difficulty getting ex-performers to acknowledge the emotional cost of the job – the toll it took on intimacy.

Curiously, within this tawdry world he also found perverse instances of innocence too, whether it was the woman who'd hung on to the DVD of Dr Butts III because it recorded the first time she'd had sex with her husband ("It's sentimental") or the actors he caught flirting shyly together in a shower after they'd finished their scene. The sex might be horribly mechanical, but he didn't lose sight of the fact that it's still humans who perform it.

A Ventriloquist's Story: Her Master's Voice was centred on a perfect Theroux subject, a vents' convention in Kentucky to which Nina Conti travelled with the puppets left to her by her mentor and lover, Ken Campbell. In its way, this too was a study of the psychological tolls of performance and self-exposure, with Conti musing on the odd business of out-sourcing part of your consciousness to a glove puppet. But it was a lot of other things besides – an odd, often uncomfortable film that dared to go to some very dark places.

Conti lay in bed at one point talking to herself about an abortion she'd had, delivering one half of the conversation in the person of her dead lover. At another she staged the "death" of her own sidekick monkey, dissolving into alarmingly plausible grief. I'm not convinced she'll ever be a great ventriloquist, but there was a risk and rawness here that I think would have made Ken Campbell proud.