Deck 6: Mpeg Video Coding I -- Mpeg-1 and 2, Basic Audio Compression Techniques, Mpeg Audio Compression, Computer and Multimedia Networks

Question 1

Work out the following problem of MPEG motion vector search in detail.
The Target (Current) Frame is a B-frame. The size of macroblocks is $4 \times 4$ and the search range is the entire picture.
The macroblock in question (darkened) in the frame has its upper-left corner at $\left(x_{t}, y_{t}\right)$ . It contains 12 dark pixels, each with intensity value 10. the other 4 pixels are part of the background, which has a uniform intensity value of 100 . There are obstacles in the scene having light pixels with value 50 .
The complete scene is described in the figure.
What is the best motion vector for coding this frame?

Answer 1

Not Answer

Question 2

Speech coders using block-wise coding usually introduce delays. If the length of the speech analysis frame is 25 msec, give a reasonable estimate of the delay on the receiver side.

Answer 2

The encoder has to wait until a whole frame has been collected before processing; this introduces a $25 \mathrm{~ms}$ delay.
Pitch analysis usually needs at least one frame buffering for smoothing. Adding the times for encoding and decoding, the delay is usually $3 *$ frame\_size $=75 \mathrm{~ms}$ .

Question 3

What is the compression ratio of MPEG audio if stereo audio sampled with 16 bits per sample at $48 \mathrm{kHz}$ is reduced to a bitstream of $256 \mathrm{kbps}$ ?

Answer 3

6.0

Question 4

In MPEG's polyphase filter bank, if $24 \mathrm{kHz}$ is divided into 32 equal-width frequency subbands,
(a) What is the size of each subband?
(b) How many critical bands, at worst, does a subband overlap?

Question 5

Both UDP and TCP are used in the Transport layer in TCP/IP networks. Discuss the differences between UDP and TCP.

Question 6

Multiplexing enables users to share the capacity over a physical link. How does FDM (Frequency Division Multiplexing) work?

Question 7

Switching is important for interconnection of telephone networks. What are the two main switching technologies? How do they work?