MediaLab can play video files while displaying a scale item for participants by using the Backvideo field in the Scale Reponse item. Specify the pathway to the desired video file in the Backvideo field and use the appropriate parameters to define the video placement and size on screen as described here in the MediaLab manual:

http://www.empirisoft.com/medialab/h...ebackvideo.htm

The trickier part comes in with displaying scales at particular points in the video file. MediaLab will stop playing the any video file in the Backvideo field as soon as it detects a valid response to the Scale Response item type. So there are wrinkles depending on how long you wanted the video to play while also showing the scale onscreen, as well as if you wanted the video to play after participants made a valid response to the scale.