I was working on a project recently and inserted a video onto one of my Storyline slides using the step above. Upon previewing the slide, I saw that a portion of the video needed to be trimmed. Fortunately, trimming a portion of a video is just as easy as inserting a video... and you don't have to leave the Storyline application.
First, select the video on the slide. Next, click the Video Tools Options tab on the Ribbon.
At the left of the Ribbon, click Edit Video to open the Articulate Video Editor.
Once you're in the Video Editor, click Trim.
By default, the first and last half-second of the video is selected for Trimming. All that you need to do now is extend or reduce the Trim Start and/or Trim End markers as needed to specify the areas of the video that need to be trimmed.
When you're done, click Save & Close and the video is trimmed. It can't get much easier than that.