Controlware Communications Systems

You are here:Knowledge Base  » Security articles » CCTV video compression  » MPEG-4

MPEG-4 CCTV video compression

MPEG-4 is a compression standard that was introduced in late 1998 by the Moving Picture Experts Group. In video surveillance applications MPEG-4 Part 2, also known as MPEG-4 Visual is the version of MPEG-4 most commonly used. MPEG-4 supports both low-bandwidth applications and those applications that require high quality images, with virtually unlimited bandwidth and no limitations in frame-rate. Typically most MPEG-4 based encoders and cameras support video up to DVD quality.

MPEG-4 is much more efficient than M-JPEG because video frames are analysed prior to being sent across the network. The first compressed image (I frame) is used as a reference point, the following images only contain information that differs to the initial I frame reference image. Periodically I frames are transmitted within the video sequence to ensure a recent reference point. The distance between these I frames is known as the GOP (Group of Pictures). The distance between I frames is usually user definable depending on the application and activity in the scene. For example a 25 FPS video stream with a GOP of 50 would mean a new I frame with GOP change information is sent every 2 seconds. The viewing application on the receiving end of the transmission then reconstructs all images based on this information and displays the video.

Advantages

• Uses less network bandwidth when compared with M-JPEG
• MPEG-4 up to 5 times more efficient than M-JPEG at low bandwidths
• Reduces the amount of storage needed compared with M-JPEG at higher frame rates
• Increases the amount of time video can be stored compared with M-JPEG
• Very efficient at high frame rates

Disadvantages

• Low efficiency at very low frame-rates or extremely high scene activity
• Can be liable to “blurring” on freeze frame or very high motion
• When the bit-rate is limited video quality suffers

• Motion JPEG
• H.264