Whenever elements on a page are likely to move, implement a system to control the movement.
Including play and pause buttons is sufficient. You could include both actions in the same button, which is updated dynamically.
Some standard cases of moving content:
Whatever the visual position of this button on the page, it must always be placed before the animated elements in the DOM. With a multimedia player, make sure this button is the first focusable element of the player.
You don’t need a pause button for moving elements which stop automatically in five seconds or less. For example, a progress bar.