The reason your video does not fit the screen is because you edited it in some ratio other than 16:9, which fills the entire YouTube player. Anytime you upload a video to YouTube that will not fill the player, YouTube will automatically add horizontal and/or vertical black bars to fill the player. This greatly reduces the viewer experience, and thus effectiveness of your video.
So what can you do to avoid this? The easiest way is to always record and edit in HD, this way you get that 16:9 ratio throughout the process. When you bring the video into YouTube, there is no conversion needed and thus the quality will always be as pristine as possible.
If you don’t have the right equipment or editing software to do this, the best thing to do for business web video is to leave it to the experts and hire out your project. Remember, how someone sees you in your video will directly correlate with how they view your business–Professional vs Amateur. If your fine with being viewed as anything less than THE person to call to solve a problem, then low quality can and will do the trick.
But most people we work with want the highest quality possible because that first impression is so important, especially online where the competition is fierce. You must always be one step ahead of your competitors.
So don’t get black barred. Either learn how to properly edit and upload your business web videos or let someone who does do it for you. The extra effort either way will pay off big in the long run.