Y’ Y’ Y’ Y’
MP4
H.264/AAC
Cb
Cr
FIGURE 5: Steps in streaming video: encode, transport, decode.
14 I ICT TODAY
Loop Out to
Local Display
Encoder
Encode Decode
Decoder
HDMI
Encapsulated
Video
RGB
Brightness (Y’)
Color (Cb and 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 determines
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 210, 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.