There are 3 major factors to consider.
Video Viewability
The best way to achieve high viewable duration in a way that is respectful of user experience (and even complements it) is with the collapsing unit. You can see it used by all of the top publishers and social platforms. This tactic simply enables the user to keep scrolling and watch the video at the same time.
Size Considerations
Obviously, a bigger video unit promotes user involvement and advertiser revenue. However, if it’s made too big, or too big for its placement, it can harm the user experience.
For the same reasons, it usually is not advised to place the unit on the side rail. Placing the video unit on the side rail limits the possible size of the unit, as the side rail is usually limited to 300px. An additional reason to avoid side bars is that they are usually considered places for ads, which is why users may apply ad blindness, and you will miss out on a great opportunity to engage your users and keep them on the site longer.
Content-Related Considerations
If the content is not created for the specific article, but is instead promoting videos you want the user to discover, then it is better to let the audience start by focusing on the text, and then give them recommendations for more related videos afterwards. That will help avoid any increase in the bounce rate. When he is well on his way, you can politely suggest content that is related to the user’s interests, and the context of the page.
Video: A Strategic Growth Engine
It all comes down to the way you regard video on your site. If you consider it as just another ad unit that will make you a few bucks, you are really missing out on the power of video to engage your users, deliver them true value, and subsequently deliver advertisers a quality high impact advertising opportunity. On the other hand, placing video at the core of your growth and revenue diversification strategy, understanding that online users demand it, and that it offers advertisers one of the most engaging ad placements, will truly transform your website.