Content control refers to the play, pause, rewind, fast forward and volume functions on videos. These are used to control the playback of any audio visual content. They can be employed by people with hearing impairments to pick their way through video or audio content at a pace which would allow them to read the captions properly if they were moving very quickly. They can also be used to rewind content where the viewer has not heard the audio properly the first time and wishes to repeat the section.
See the image below with its content controls at the bottom. Note that there is a slider which replaces the rewind and fast forward functions to move the video back and forth.