Translation:The movie was just about to start when everything became black.
As a native Swede I can hear what sounds good (of course), but when I start thinking about the placement of a sentence adverb I realize that it is complicated.
In the sentence above, we have a helping verb "skulle" and a main verb "börja". Then, the adverb normally takes the position between the verbs:
Vi skulle precis börja
Han ska inte börja
Hon har ju börjat
De vill antagligen börja
So precis is modifying börja. That helps, but the contrast between the precision denoted by the word precis and the indefiniteness of the film being about to start (maybe in 2 minutes, maybe in 3) is a little jarring. I thought that everything went black because they put out the lights to watch the film. Apparently even the projectionist was surprised by the darkness. And I agree, your replacement suggestion does not sound natural. (Am I overthinking this?)
I'm not sure you understand it correctly. precis has a temporal meaning that is much like 'just' in English. In this meaning, there isn't really a very strong feeling of 'preciseness' in it.
You can say things like Jag har precis ätit 'I just ate'
or Vi ska precis gå 'We're just about to leave'
– but just like you don't really feel the meaning "only" in the English "just" here, you don't really think that much of "preciseness" for the Swedish sentences. You could also have said ungefär nu – 'approximately now'.
The situation in the sentence is like this: the movie is supposed to start, but it never actually starts, because the lights go out instead. There was probably a power outage. As you say, even the projectionist is surprised.
So 'precis' is not 'precisely' then, but 'just'. Then, how does 'bara' differ from 'precis'. Duo did not accept: 'the film was going to start precisely when everything became black' as translation for this sentence. Could you please explain how to differentiate 'bara' from 'precis'?
I intended one (the audience in the theater might not notice if the film was being threaded - that's why I wanted to make mine independent of the process). But I make it "Right before the film would begin." Your translation is a before-before construction, which I agree is quite different from the original sentence (which is what I'm trying to get close to). There are a lot of possible scenarios here, timewise, and maybe very different constructions for each?
Yes, maybe that's a better translation. It's a change in perspective either way just because you say 'X happened before Y' instead of 'Y was happening/started to happen/whatever when X happened' so it still strays too far from the original sentence to be an accepted translation. Other than that, I'm sure there can be a ton of different situations and constructions here with different connotations.