Welcome to Android Central! Is this for streaming video in the browser, or on an app like YouTube or Netflix? Or is it for locally stored video files, being played by a video app?
Not sure if this will help, but go to Settings>Developer Options, and look for an option to toggle between NuPlayer and AwesomePlayer. Toggle it to the other option, and see what happens.
There are a number of questions about this recently, so there might be a glitch specific to the S6. Try wiping the cache partition: https://support.t-mobile.com/docs/DOC-21095