https://support.vhx.tv/article/628-how-do-i-adjust-the-volume-of-my-video-player
If the volume for a video appears to not be working when your computer volume works, you may want to check the video volume itself (see picture below).
If the blue bars are not there but gray, please click them to make them blue, so that the video volume works. If the blue bars are appearing, the video sound is on as well, so you may want to restart your computer and see if it works.