Why are the movies going dark/dim

Using captivate 8. When viewing the training on Chrome / HTML5, the videos start out fine, but then after a few seconds, they dim.

The movies are usually under 2 minutes and they originate in mp4 when I import them into the slide.

While in captivate, clicking the timeline play button, it does not play the video for me. (not sure why but I am not too concerned at this point)

When using the dropdown preview / next 5 slides, it plays just fine. (I believe this is the swf version of the presentation)

When using the dropdown preview / html5 it opens it in internet explorer, and when publishing to html5 and opening it in Chrome, the video starts out fine but then after a few seconds, the video dims.