System Configuration : Preferences : Operation Preferences : Video Section

Video Section
High Quality QuickTime Image (DV25 Only)
When enabled, Pro Tools decompresses both fields of each interlaced frame of QuickTime video. When not enabled, Pro Tools only decompresses one field of each frame for “half-res” QuickTime playback.
When viewing a QuickTime movie in the Pro Tools Video window, select this option to display the movie at the highest possible resolution. For interlaced video that was transcoded from a progressive source, enable this option for a crisper image. Deselecting this option can help improve performance if your system experiences problems playing back a session with QuickTime video.
Avid Video Errors Stop Playback
(Pro Tools HD with Avid Video Engine Only)
When selected, Pro Tools automatically stops playback of audio and video if a single frame of video is dropped.
When not selected, Pro Tools continues playback of audio even if frames are dropped. In most cases, video playback will recover within a few frames and continue playing audio and video in sync.
Avid Video NTSC Has Setup (NTSC-J)
(Pro Tools HD with Avid Video Engine Only)
This preference lets you adjust the level of NTSC video black output between 7.5 IRE (standard) or 0 IRE. When this option is selected, output level is 0 IRE.