Subtitling is a complex process which entails:
Material analysis and preparation for the subtitle insertion.
Text translation, taking into account what is written on the film script and what is shown on the screen.
Subtitle editing, to check they are linguistically correct and fit into the limited space and time required to display the captions.
A thorough review to ensure that the subtitle is in perfect synch with the image, so that the subtitle is displayed in the exact moment and during the exact time.
In the case of Closed Captioning, analysis and adaptation of the audiovisual contents are necessary to make them suitable for their screening on movie theatres, festivals, public or private TV stations, and for the deaf and hard of hearing people.
The closed captioning technique also includes the description of sound effects, tones of voices or ways of speaking.