In both the Viewer and Compositor windows, there is an arrow on the right hand side of the other
buttons in the edit panel as shown in figure 2.18Viewer Window - the red arrow "Play" button is left of the Videoscope button. The "play" button can be
toggled on/off via this arrow, which has a tooltip of Click to play . When enabled
the arrow is white surrounded by green and when disabled the arrow is red.The purpose of enabling this capability is to make it really easy to play the media in the window
by just using the left mouse button to start or stop the play. The entire main canvas surface
becomes a big play button! Although the default is initially off, a good reason to enable this,
at least temporarily, is so that you can quickly review your video before a render.