Media selection
Media selection involves streaming type and the choice of codec used.

Streaming type
IP media devices can stream video and audio over IP using several IP protocols and protocol combinations such as HTTP, Real-Time Transport Protocol (RTP) and Real-Time Streaming Protocol (RTSP). These protocol combinations may be transported over TCP, a connection-oriented protocol, to assure delivery, or UDP for improved performance.

An IP media standard must support all combination of protocols to allow cameras to be deployed in a variety of networking environments.

Codecs
In order to store and view video, the video stream must be digitized. A video stream consists of a series of still images or frames displayed in rapid succession. In North America, real-time video is reached when 30 images are displayed to the viewer in one second (30 frames per second), which is known as NTSC (National Television System Committee). North American televisions receive and display video at this rate. In Europe, however, the rate is reduced to 25 fps -- known as PAL (Phase Alternating Line). Each still image is a rectangle consisting of an array of picture elements also known as pixels. Pixels represent the light intensity that a camera sees in either black and white or color. Standard definition TV displays at 720 x 480 usable pixels, providing what is known as a 4 x 3 aspect ratio. The newer HD televisions have a much higher pixel count. For example, 1080p has an image resolution of 1920 x 1080 pixels.

In order to create a digital video stream, light must be converted into values that can be transmitted. This is done using light sensors. A light sensor responds to the intensity of the light it "sees" and returns a voltage signal. In black and white cameras, each pixel can be represented by a separate light sensor. In color cameras, however, the sensors are grouped together in threes. There is one for red, green and blue (RGB), since the combination of these colors in different variations can produce any other color.

The voltage provided by the sensors is converted to discrete digital values by use of an analog to digital converter (A/D). The A/D converter takes in the voltage and converts it to an 8-bit value, resulting in 8 bits for a simple black and white pixel, or up to 24 bits for a color pixel.

As stated previously, video is just another form of data, so why should IT professionals worry about it anymore than any other traffic that uses their network? The answer is volume. Transmitting video over a network can be expensive in terms of bandwidth utilization. When more bandwidth is consumed by video, less is available for other applications such as voice, data and mission-critical systems. In addition to this, transmitting large video streams can become cost-prohibitive over WANs where usage charges may apply. To reduce bandwidth utilization, IP media devices compress video using different compression techniques and codecs.

Codecs offer a tradeoff between video compression and performance. Early IP cameras offered MJPEG compression where each image was compressed and transmitted. While these cameras provided impressive resolution capabilities, the bandwidth and storage requirements imposed limited their usefulness. MPEG4 can reduce the data stream and storage requirements by up to 50% over MJPEG, while H.264 codecs can yield additional performance gains of up to 30%. The tradeoff for these significant compression improvements is revealed in terms of processing performance. More powerful processors or Digital Signal Processors (DSP) are required to handle MPEG4 and H.264.

IP cameras, with their distributed computing capabilities, allow IP VMS solutions to scale. By moving the digitization and compression of video signals to the edge, customers can choose the optimal codec for their implementation. The choice of codec is important as processing-intensive codecs can significantly reduce bandwidth and storage requirements. With Moore's law in effect, IP camera processing performance has increased and will likely continue to increase, while cost will likely continue to fall. With falling prices, IP cameras have undertaken more CPU-intensive tasks, including analytics processing and advanced compression algorithms like H.264.

While standard variants of MPEG4 and H.264 codecs exist, many vendors have implemented specific performance enhancements that require the use of vendor-specific codecs.

Some IP cameras or encoders also support audio and are equipped with a microphone or microphone input. Audio is encoded in one of several formats e.g. G.711, G.726, G.729, MP3. Like video, the choice of audio codec will depend on the audio quality required and available bandwidth and performance.

An IP media device standard should allow the negotiation between a VMS solution and an IP media device to occur so that compatible audio and/or video codecs can be selected automatically. IP telephony addressed this problem by using the Session Description Protocol (SDP) media-level information exchange to ensure interoperability.

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