In order use captions for video or audio you have to create a subtitle first. Subtitles are a kind of container which contains the actual captions.
The subtitle contains information about the language or the publication status.
Reference
Find subtitles
Returns all subtitles for a given mediacontainer
Create a new subtitle
Creates the subtitle file which is the basis for 1-n captions.
Update an existing subtitle
Update subtitle file with a different name or language or publish state.
Delete a subtitle
Destroys a subtitle file including all captions! This will permamently delete the subtitles and all captions!
Duplicate subtitle
You can duplicate a subtitle including all captions with a single call. You can use it to prepare a translation document for a new language.
Import Subtitle
In order to import a subtitle follow the tutorial “Import subtitles”.
Export Subtitle
Export all captions for a given subtitle. Please note that this is still beta.