Chap.3 Video and Audio Compression
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3.3 Video and Audio Streaming
3.3.1 Multiple Streams
Multiple streaming allows each video stream to be delivered in a different resolution, frame rate, and image quality
for individual quality or bandwidth demands. As a result, the camera can simultaneously transmit a small image
in CIF format for real-time monitoring and a large megapixel image for storage. The CIF image can be directly
displayed on the screen without much decoding or further scaling, thereby drastically reducing CPU loading. In
addition, because different devices such as PCs and mobile phones have different requirements for image sizes,
resolutions, and frame rates, multiple streaming gives users a higher level of flexibility for dealing with camera
images on different platforms. (Figure 3.6).
3.3.2 Two-way Audio
Generally, audio transmission methods consist of simplex, half duplex and full duplex. Unlike simplex and half
duplex, full duplex provides simultaneous communications capability, also known as two-way audio.
Simplex
Voices can be transmitted in one direction only, from the sender to the receiver. For example, only the control site
or the monitored site can make announcement; the receiver cannot make any response.
Network Camera
3G Cell phone
176x144 MPEG-4 5fps
640x480 H.264 30fps
1600x1200 MJPEG 15fps
Desktop PC for Viewing and Storage
NVR for Storage
Figure 3.6 Multiple streams are sent with different configurations simultaneously
Figure 3.7 Simplex allows only unidirectional communications
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