You can lock one or more video tracks to prevent any video clips on those tracks from being edited.
When a video track is locked, Pro Tools restricts all editing operations involving the track (except for locking and unlocking video clips).
A locked video track displays a small lock to indicate that the video track has been locked and cannot be edited. (The lock does not appear if the Track Height of the video track is set to Mini.)
Locking or unlocking a video track does not alter the lock status of individual clips. If a clip was locked before you lock the track, the clip will still be locked when you unlock the track. However, unlocking a clip in a locked track will not allow you to edit that clip. It will behave as if the clip were locked until you unlock the track.