Video and Audio Problems when I open Zoom

There are numerous ways to share a video with Zoom. so I am going to assume that you did a screen share of the media player. The playback volume is controlled by the media players volume control and your computer systems speaker volume control. If you turned down your speaker volume control on your computer then you also turned down the playback volume control to your Zoom audience. Using speakers or headphones with their own separate volume control will help.

If the video someone else is sharing appears blurred it is most likely the result of insufficient bandwidth of the sender or the result of you using a weak WiFi signal that is substantially reducing your download bandwidth.