It can be useful to include an external video in the visualization of your results - for example, you may have a video of an experiment that you want to show together with the analysis of the simulation data. This can easily be done in EnSight.
In the viewport, create an annotation Shape, with Shape = rectangular. In the annotation edit window (that you can open bu right-click on the annotation -> Edit), click on "edit texture". This will open the texture widget. Right-click on texture 1 -> load texture. Choose your video file. Then, Save.
In the rectangular annotation window, set now Texture to be texture 1. You will see in the viewport that the rectangular annotation is, indeed, your video file. If you change timestep, the annotation updates.
By default, the annotation will update so that the timestep = 0 of the dataset is the first frame of the video, and the last timestep of the dataset is the last frame of the video.
You can drag / reshape the annotation as you wish on the viewport.