Like they match the general gist of each other but not very close.
In: 5
Other answers already have most of it, but one additional consideration is speaking time. Not just matching mouth movements, but the time it takes for someone to deliver their line.
Some languages tend to be more information-dense than others, and some dialects are spoken at a pretty fast clip. If a line delivered in Chinese would take twice as long to say in English, they’re going to have to take some liberties to get the same information across in the limited time before the next character starts speaking, or the next scene transition, or… etc…
But since people read faster than they speak, you don’t have to bother with rephrasing subtitles if you don’t want to. You can just put up an exact translation.
Additionally, subtitles are done for the original distribution of the film, while a dub is a larger production to make a localized version. The original subtitles are often written before the dub exists, and the dub is recorded with additional considerations that often require changes to the script. They *could* go back and re-subtitle the original to match the dubbed version, but if someone’s choosing to watch the subtitled version over the dub, they probably want to read the closest translation, not a hacked up version.
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