Download the 1080p or 4K version of the film first. Match the frame rate (usually 23.976 fps) with your subtitle file. Using mismatched timing will ruin even the best Idiocracy Vietsub.
When looking for the best Vietnamese subtitle file, do not settle for machine translations (Google Translate or ChatGPT subs). Here are the three tiers of Vietsub quality: idiocracy vietsub best