Trouble with Videos and Slide length?

Hi there! I'm in major need of help so even if anyone else has had this problem before would be very good to hear, in the sense that even though it'll take longer to edit I can still make the slides work.

I work for a technologies company making training courses. One such course has two slides, the first of which contains only a video. The videos are of varying lengths and had to be trimmed a bit to get rid of unwanted copyright redundancies at the beginning or end. I was informed, after sending these off, that there was a rather long bit of dead air at the end, where the audience was simply subjected to a blank screen for upwards to three minutes. I went in today to check what was wrong and couldn't find a blasted thing. The slide was saying that it was the exact length of the video, but when I played it back there was quite a lot of dead air at the end. I went in to trim the video further, but Storyline simply crashed on me. Twice. I nixed the idea and instead took the length of the video as read by Storyline and compared it to the slide length, trimming it accordingly. I don't believe the calculations of time were correct, however, because there was still a full minute and one half of dead air. I would assume I'd simply read the numbers wrong, having had trimmed the video within Storyline, but I'd only trimmed a few seconds off the very end, so I can't imagine that would be the reason behind it? I could be wrong, though. I really hope someone can help! I've been using a stopwatch to actually time the amount of dead air and then trimming the screen accordingly. Please let me know, thank you for your time reading this!