The requirements for the dimensions of your cover video are least 820 x 312 pixels.
Ideally, your Facebook cover video length should be between 20-90 seconds. It’s like a mini-advert playing continually on a loop.
When users visit your page, your Facebook cover photo is one of the first things they’ll notice. For new visitors, your cover photo can help represent your brand and portray your story in just a few seconds. It only makes sense that a short video can accomplish this better than a still photo.
Video immediately grabs the audience’s attention. Just like in the news feed, a cover video will autoplay (without sound), drawing users’ eyes right to it. This may help keep visitors on your page and simultaneously drive more engagement.
Your cover video will be more effective if it gets its point across without sound. If users click to enable sound, great! But if they don’t, you haven’t lost anything.