Axis IP-Surveillance system Design Manual page 15

> Type of video compression: There are three main video compression standards in use today:
Motion JPEG, MPEG-4 Part 2 (also referred to simply as MPEG-4 in some references), and H.264
(also known as MPEG-4 Part 10/AVC). Each standard employs different techniques to reduce the
amount of data transferred and stored in a network video system.
H.264 is the latest standard that is expected to become the video standard of choice in the
coming years. Without compromising image quality, H.264 can reduce bandwidth and storage
requirements by more than 80 percent compared with Motion JPEG and as much as 50 percent
more than with the MPEG-4 Part 2 standard. H.264 and MPEG-4 Part 2 are licensed technologies,
so if a network video product supports those standards, be sure to find out if the license fee is
already included in the product's purchase price. H.264 and MPEG-4 Part 2 provide support for
synchronized audio, while Motion JPEG does not. Motion JPEG is an unlicensed technology.
For the time being, network video products that support multiple compression standards are ideal
for maximum flexibility and integration possibilities.
> Video resolution: A VGA resolution is 640x480 pixels. (Computer screens have resolutions in VGA
or multiples of VGA.) Another common format is 4CIF (704x480 pixels in NTSC / 704x576 pixels in
PAL standard). Megapixel cameras provide high resolutions of at least 1280x960 pixels and are
used for applications that require the ability to see fine details or cover a large area. A network
video product's ability to deliver a specified number of frames per second may vary depending
on the resolution.
> Frames per second: There may be different frame rates specified for different resolutions. Full-
motion video is 30 frames per second in NTSC video standard (in North America/Japan) and 25
frames per second in PAL video standard (Europe). Full frame rate on all cameras at all times is
more than what is required for most applications. With the configuration capabilities and built-in
intelligence of network cameras, frame rates under normal conditions can be set lower, e.g. one to
four frames per second, to dramatically decrease storage requirements. In the event of an alarm—
for instance, if video motion detection or an external sensor is triggered—a video management
software program can be configured to request that the network video product send a different
stream with a higher recording frame rate.
> Multiple, individually configurable streams: Network video products with this capability can
provide multiple streams and each stream can be configured differently in terms of compression
format and level, frame rate and resolution. For example, one stream can be configured with
maximum compression and low frame rate for storage purposes; another stream can be sent with
higher frame rate and less compression and, therefore, less lag for live viewing; and a third stream
with high compression and low resolution can be sent to mobile devices.
Analog camera
Video encoder
Figure 2.1.p. Multiple, individually configurable video streams
1 second
Remote recording/
viewing at medium
frame rate and
medium resolution
Local recording/
viewing at full
frame rate and
high resolution
Viewing with a
mobile telephone
at medium frame
rate and low
resolution
15