Issue link: https://www.e-digitaleditions.com/i/1156106
14 I ICT TODAY FIGURE 5: Steps in streaming video: encode, transport, decode. Loop Out to Local Display Encoder Encode Decode Decoder HDMI Encapsulated Video H.264/AAC MP4 RGB Brightness (Y') Color (Cb and Cr) Cb Y' Y' Y' Y' Cr Cb Cr Cb Cr Cb Cr Brightness (Y') Color (Cb and Cr) Compressed Compressed RGB Process Process Compress De-compress Encapsulate De-encapsulate HDMI LAN/WAN Internet • Color Bit Depth—This is the number of bits per pixel representing the level of red, green or blue primary colors comprising the pixel, and it deter- mines how finely levels of color can be expressed. For example, 10-bit depth means that each red, green or blue color component of a pixel has a value of 2 10 , or 1024 values. This allows a pixel to display 2 (10*3) = 1.07 billion colors. Reducing the bit depth for compression lowers the amount of data required; it also reduces color fidelity. • Temporal Compression—In many video motion sequences, a small percentage of pixels differ from frame to frame. It depends on the content; action scenes have more changes between frames and therefore compress less than static scenes. Temporal compression digitizes the entire content of the first frame in a series, called a key frame. In one or more subsequent frames, called delta frames, only the information that has changed is digitized. The compression algorithm determines when the image has changed enough to initiate the next key frame, followed by another series of associated delta frames. Steps in Streaming Video Streaming compressed video across an Ethernet network is a three-step process: encoding, transmission, and decoding. • Encoding and Decoding—Encoding entails compressing the RGB video signal using a set of algorithms defined by the codec employed, then encapsulating the compressed video in a container for transport over the network. The container stores bytes from the codec in a standardized format that can be recognized by the decoder, which reverses the process. In the example shown in Figure 5, the encoding process uses the popular H.264/AAC codec to compress the RGB video. Then, the compressed video is encapsulated in an MPEG 4 When streaming video over Ethernet, unicast and multicast are two commonly used methods to transmit from source to destination.