Canon EOS-1D X Mark II Manual (en)

You can adjust volume during playback with the volume slider.
You can change the movie playback speed.
Drag the volume slider left or right.
To temporarily turn audio off, click the [ 
 ] (mute) button.
Click the [ 
 ] button while a movie is played.
Each time you click the [ 
 ] button, the playback speed 
You can change the playback speed on the screen displayed by 
selecting [EOS MOVIE Utility] menu   [Playback speed 
Audio is not played during playback when playback speed is 
other than x1.0.
Adjusting Volume
Volume slider
Mute button
Changing the Playback Speed
Playback speed 
adjustment button
playback speed
You can move the playback position with the frame position slider.
Drag the frame position slider left or right while a clip 
is played or stopped.
Moving the Playback Position
Frame position slider