Inadvertently move the video when moving view

[avpromedia]

Holding down the space bar allows you to pan around the screen which is useful when zoomed in working on masks.

However, sometimes I found, after I zoom to fit, that the video and the masks both moved off screen partially.

I guess I must have clicked on the wrong thing but can't figure out what. What is the most likely cause for the video to move off screen when I'm trying to move the view?

Is there a way to lock the video to the "canvas" so it cannot be moved off screen accidentally?

[Warren Heaton]

Layers can be locked to prevent most unwanted changes.

To lock a layer(s):

• Use the corresponding Lock Switch located with the AV Switches in the A/V Features Pane of the Timeline Panel.
• Select the layer(s) and then use use the keyboard shortcut command + L (macOS)/control + L (Window).
• Select the layer(s)  and then choose Layer > Switches > Lock while the layer is selected. 

Lock Switch located with the AV Switches in the A/V Features Pane of the Timeline Panel