Play
Starts playback or (if the Record button was clicked first) recording from the Timeline insertion point or the Play Start Marker location if Dynamic Transport mode is enabled.
You can also begin playback by pressing the Spacebar, or with the Numeric Keypad mode set to Transport, pressing 0.
Right-clicking the Play button lets you select the playback mode from a pop-up menu:
• Normal
• Loop
With the Transport stopped, Control-click Play (Mac) or Start-click Play (Windows) to toggle Loop Playback mode. When enabled, a loop symbol appears in the Play button and Pro Tools plays continuously from the beginning of the selection to the end.