In a vacuum IP cameras are more powerful than their analog/CCTV cousins. However the strength and reliability of a network can bring an IP camera to its knees if the proper amount of bandwidth is not available to handle the information being processed.
A reason why IP cameras are gaining in popularity is because network infrastructures are constantly growing in size and capabilities as are internet speeds. Just like uploading or downloading images or video to/from the internet, speed plays a crucial role in the quality of that experience. The same goes for accessing stored or live images from your computer’s network or, accessing them remotely via the internet.
Were it not for compression formats known as codecs (coding-decoding), digitized video which consumes hundreds of Mbps (mega bits per second) worth of bandwidth, would not be practical to transmit over an IP based network and would be costly in terms of amount of space need to store the data.
So, various compression formats have been developed to reduce large amounts of redundant information.
Video Compression Formats
The most common video compression formats used today are:
- Motion JPEG (M-JPEG): Represented as a series of of JPEG images.
- MPEG-4: The next generation of MPEG (Moving Picture Experts Group) that supports low-bandwidth consuming applications (such as cell phones) and applications that require high quality images and with virtually unlimted bandwidth.
- H.264: The latest standard for video encoding that provides good video at low bit rates.
Many IP cameras are designed to handle multiple compression formats for different applications such as the Axis M1011-W with individually configurable video streams in Motion JPEG, MPEG-4, and H.264.
Another example is the Sony SNC-CH210 which also supports all three codecs and offers “Dual Streaming” capability which allows for any combination of JPEG/MPEG-4/H.264 including multiple streams of the same format.
Variable and Constant Bit Rate
An important aspect of compression formats is the bit rate used and oftentimes it is possible to select the rate: constant bit rate (CBR) or variable bit rate (VBR). Bit rate is simply the rate (in a given amount of time) at which bits (data) are transferred from one location to another.
With limited bandwidth the preferred mode is CBR because this mode generates a constant and predefined bit rate. The downside is that the image quality will vary depending on the amount of motion in the video scene. No motion = high image quality. Increased motion = low image quality (the more movement in a scene, the more data being transferred).
When there’s a need for high quality images and the network infrastructure has a high capacity, VBR is the desired bit rate. When there is motion in a scene image quality can be maintained because the bit rate is allowed to vary to achieve this high quality and because the network has the available bandwidth to handle it.
Network Desgin Considerations
Depending on the level of quality you’re looking to get out of your surveillance system, different compression standards and configuration can and should be considered. No single standard fits all solutions.
- Frame Rate: What’s the required frame rate? Below 5 fps Motion JPEG is a good choice and can be controlled by video motion detection on the camera. For higher frame rates MPEG-4 is best for it’s bandwidth and storage saving ability.
- Bandwidth: What’s the available network bandwidth? Consider CBR vs. VBR and remember that image quality may suffer when there is motion.
- Image Quality: What’s the acceptable level of image degradation allowed for your application? Compression ratios above 90% can be used if the scene is not terribly complex.
- Latency: How much latency (time) for the compression process is allowed? PTZ IP Cameras need low latency for their live images but, if video is only recorded latency may not be an issue.
- Robustness: How robust/secure must your system be and what is your budge for this system? Is it acceptable for video to be lost for X amount of seconds if the network drops a frame?
- Standard & Compatibility: Is openness of your system and compatibility with other systems important for the ease of use you’re looking for? If so, be certain you choose products that follow the standard 100%.