When I load a video i am only getting a black screen.

I agree with Rod, if you are testing from within Captivate with scorm cloud on the functionality. The first question I have is your use of the term video, are you talking about a published Captivate project as a swf or html5 output, or are using video to mean an MP4 file. I have students who confuse this terminology all the time. I think this is a holder over from the old Flash movie or video days.

I'm guessing if this is an MP4 video file and it is 79 minutes plus it must have some bulk in terms of file size which could cause the failure to play. You also may want to see if your LMS can actually handle the file if it sizeable because I have worked on LMS's where surprisingly there is a very small file size limit for videos.

I just want to clarify though, is your video playing in a Captivate slide as event video or embedded video, or is it a standalone MP4 file that you are putting in your LMS as a video.

If you are placing it in Captivate slides,  you may want to consider using Premiere to slice it up to make it into more manageable chunks. This may help to ensure that the video will play.

If you are talking about Captivate's built-in Preview in SCORM Cloud option, that has very limited functionality.

For a more accurate idea of what will work, publish your project out to SCORM and then upload the entire zip to SCORM Cloud itself and see what happens.  Does it only show a black screen then?