there are different ways you add text to already shown subtitles:  - the first one, you show the whole text at the start of a sentence. - the second one, you add words to the text and , if it's centered, it changes position on the screen - the third one, you add the whole text but it's masked and then you add words to that mask  so, here's my question: how do you decide which method to choose?
the second method you mentioned, in my opinion, always feels terrible and i never do it (unless by mistake). and the third one you mentioned i didn't understand your description. but here's my basic theory for it. first, some terminology... "word pops" is when the words appear one at a time. "cumulative word pops" means each new word appears, with the previous words staying there. "replace word pops" is when the new word appears and the old word disappears, with only 1 word ever on screen at a time. "entire phrase pop" is when multiple words appear at the same time. Generally, in my opinion, when doing cumulative word pops, it's very uncomfortable for the staying words to move when the new word hits. this is why your second option doesn't work for me. However, often, i might want the final result to have a centered feel to it. in that case, i actually use left justify and use spaces to get the final result how i want. then i do the cumulative word pops to work toward that, so the words don't jump. "Replacing word pops" usually means the words are fairly big, maybe even full screen. Replacing-wordpops tends to be uncomfortable if it's a normal (fast) paced sentence. replacing wordpops is usually best for like a 3 word sentence where all 3 words are strong and emphasized. Otherwise, when deciding whether to do cumulative wordpops vs displaying the whole thing all at once, this is what i've noticed: alltogether works better when the sentence is an already-known quantity. a typical sentence. in other words, when i expect the viewer to already know the sentence. in other words, it's a sentence with no surprises. such as: "how are you doing?" or "i'll see you tomorrow" or "i never noticed that". It's basically a sentence that functions as one word. it's a package deal that everyone already knows. That's when it's usually best to make the whole sentence appear at the same time. But when the sentence is more unique, or has surprises in it, that's when you want cumulative word pops. Another method, for different situations, is "letter type" where it appears one letter at a time, steadily. This seems to be best when it seems to be some kind of pre-written, impersonal, formal message