sound is not playing on FB ...ok on youtube..when I play a clip the sound with a line through shows in the top bar bit even thought the mute is not on on the clip...
You haven't said whether you are using the FB app or a browser, but if you are using Chrome there is a facility to mute individual tabs. When a video or audio clip is playing, a loudspeaker icon appears in the tab next to the title. Clicking it will mute the sound (shown as a speaker with a diagonal line through it). Clicking again will unmute the sound, and the diagonal line will disappear.