From Dahua Wiki
The displayed video is not full in the monitor.
Please do the following:
1. Check your physical connections from the system to the monitor.
2. Check your aspect ratio.
3. If a VGA connection, ensure the screws are tight.
4. For the VGA connection, 25 feet or less is recommended for high resolution and 50 feet for lower resolution.
5. If a DVI connection, also ensure the screws are tight.
6. For the DVI connection, Up to 15 feet at high resolutions (above 1280x1024), or up to 50 feet at lower resolutions (1280x1024 and below)
7. If a HDMI connection, 1080p monitor is recommended.
8. For the HDMI connection, less than 50 feet is highly recommended with 25 feet or less is preferred.
9. If a DP connection, make sure the monitor is at least 1080p.
10. On the monitor check the current resolution setup. If the current setup is 1920*1080, then you need to set the monitor resolution as 1920*1080 or 1080P capable.
11. Monitor is incapable of displaying the device recorders resolution output.
Coaxial with BNC connector
HDMI (High-Definition Multimedia Interface) Connector
DVI (Digital Visual Interface) Connector
DP (Display Port) Connector
VGA (Video Graphics Array) Connector