These are the controls for a video with sound:

– This is the mute button, click to mute the audio for the video being viewed.

– If a video does not have sound there will not be a volume control.

Video without audio will not have an audio control, or will have the audio control "X"-ed out.

– These are the Play and Pause buttons, Press to begin video playback, press a second time to pause.

– Also, there is a stop button available.

This progress–bar indicates the user's current position in the video being viewed:

Audio Controls
To begin audio playback press the "play" button on the right, to stop playback press the left "stop" button.