A screen reader communicates interface information through speech or other accessible output. It depends on the operating system and application exposing meaningful controls, names and state. It can help navigate a player, but it is different from audio description within a programme and cannot automatically describe every visual event in a video.
A practical example
A viewer may hear the name and state of a playback button while moving through an accessible interface. If an app exposes only unlabeled icons, the screen reader can have too little information to explain what those controls do.
A common misunderstanding
Do not assume that a device-wide accessibility feature makes every app fully accessible. Test the actual menus, focus order and control labels in the particular application being used.
Related terms
Stable technical definition. Editorial approach