Using a custom variable you could identify those who watched the video and then view reports about them. See https://developers.google.com/analytics/devguides/collection/gajs/gaTrackingCustomVariables#pageLevel
For example when the video has ended you could execute the following code:
1, // This custom var is set to slot #1.
'WatchedVideo', // The top-level name for your online content categories.
'VideoID_123', // Identifies the unique video
3 // Sets the scope to page-level. Optional parameter.
You can then view reports of these visits in the Custom Variables section of Analytics, and you can use the values to define Advanced Segments which allows more detailed reports to be run across the Analytics tool.