LinkedIn does not support videos in comments. Use this workaround with Sendspark to share videos as links with GIF thumbnails.
Please note that GIF previews only show when you post the URL from a mobile device (the LinkedIn mobile app, mobile Chrome, mobile Safari, etc).
How to Post a Video in a LinkedIn Comment with a Thumbnail
To post your video in a LinkedIn comment, launch the Share modal through your dashboard or video edit page.
Click on Copy Link to copy the share URL to your clipboard