If video keywords is enabled in the application and you have permission to update a video then you will see an 'Add/Edit video keywords' button on the Video details page. You can access this page by searching for the asset and then clicking 'View details' in the search results.

The Update video keywords page allows you to manage video keywords for the video:

You can add new keywords for each supported language for a given point in time in the video by playing the video and pausing at the time point, the button 'get current' will populate the Start or End point. Add text to at least the English Keywords text field and click the 'Add' button to save.

To edit existing keywords, click the 'edit' link and the 'Add new keywords' form will be populated with the existing values which you can modify and then save by clicking the 'Save' button (Note: the 'Add' button becomes 'Save' once 'edit' is clicked).

To delete existing keywords click the 'delete' link.