The skill of a corporate video is to judge what is best for a project, client and thier audience. Feedback may offer some insights and industry awards should be a guide too of the quality of what is produced. Courtesy of the internet you get so much more, not only information on the audience, but on viewing patterns and feedback. You can hear what they think in many ways, not least through messaging or a Twitter feed if the content is streamed during a live event, but from social platforms and activities embedded around the content, from a simple 'rate' or 'like' this to a survey.
Effectiveness is measured as part of the assessment process which is part of the learning design. You want to rest comprehension as part of the learning process, but you also want to know how effect the learning content, of which video is a part, is being. It is an iterative process; you adjust the content as you learn how your audiences respond to the content.