8.9 Problems

8.9 Problems

1. 

Why are the systems in MPEG-2 different from those in MPEG-1?

2. 

Which of the following represents level and profile?

  1. 1.5 Mbit/s

  2. SIF

  3. SNR scalability

  4. 720 × 576 pixels.

3. 

The DCT coefficients of a motion compensated picture block are given as:

33

-10

-41

3

17

2

7

-13

61

-5

23

12

-11

5

6

-9

-3

11

3

9

-15

6

3

-1

2

-34

6

4

0

1

3

1

-21

-3

0

5

12

3

0

1

-7

-5

9

3

2

7

-1

-2

6

3

2

5

7

-2

-3

1

-5

4

-2

6

3

1

2

1

They are linearly quantised with th = q, zigzag scanned and the assigned bits are calculated from Figure 6.12. For q = 8, identify the two-dimensional events of (run, index) and the number of bits required to code the block.

4. 

The block of problem 3 is partitioned into two, and the priority break point (PBP) is set at coefficient (2, 2). Assuming that PBP can be identified with six bits, and the quantiser step size is q = 8, calculate the number of bits generated in each layer and the total number of bits. (Note the first DCT coefficient is defined at (0, 0).)

5. 

The block in problem 3 is SNR scalable coded with the base and enhancement quantiser step sizes of 14 and 8, respectively. What are the number of generated bits in each layer, and the total number of bits (assume in each layer th = q)?

6. 

An MPEG-2 coded video with its associated audio and forward error correcting codes comprises 8 Mbit/s. With a 64-QAM modulation, determine how many such videos can be accommodated in a UHF channel of 8 MHz bandwidth, with 2 MHz guard band. Assume each modulated symbol occupies 1.25 Hz of the channel.

7. 

Draw a two-state channel error model and determine the transition probabilities for each of the following conditions:

  1. bit error rate of P = 10-5 and burst length of B = 5

  2. bit error rate of P = 10-5 and burst length of B = 1.

8. 

Table 8.7 shows the duration of various parts of a 90 minute VBR-MPEG-2 coded video stored on a DVD. The given bit rate is smoothed over a GOP, but is presented in Mbit/s:

  1. calculate the required storage capacity

  2. calculate the peak-to-mean bit rate ratio

  3. calculate the storage required if the video was coded in CBR at a quality not poorer than the VBR.

Table 8.7: Duration of various picture activity in a DVD program

Duration [min]

0.5

5

10

20

30

24.5

Bit rate [Mb/s]

20

15

10

7.5

5

4

9. 

The ATM cells with AAL1 adaptation layer have a five-byte header and 48-byte payload, of which 47 bytes are used for packing the video data. If the channel bit error rate is 10-7, calculate the probability that:

  1. video is decoded erroneously

  2. the cell is lost.

10. 

The stored DVD video in problem 8 is to be streamed via an ATM network, with a maximum channel capacity of 50 Mbit/s. Due to the other users on the link, on the average only 30 per cent of the link capacity can be used by the DVD server. With an AAL1 packetisation, calculate the time required to download the entire DVD video stream over the link.

11. 

The cell loss rate of an ATM link can be modelled with , where 0 ρ 1 is the load of the link. Twenty-five video sources, each coded at an average bit rate of 4 Mbit/s, are streamed via a 155 Mbit/s ATM link, with AAL1 adaptation layer. Calculate:

  1. the network load, ρ

  2. the loss rate that each ATM cell may experience.

12. 

The video sources in problem 11 were two-layer coded with SNR scalability, but the overall video quality was assumed to remain the same. If in each source 50 per cent of its data is assigned to the base layer, and the base layer cells are always served in preference to the enhancement layers cells, calculate the cell loss probability at the:

  1. base layer

  2. enhancement layer

(hint, use Figure 8.25 for the additional overhead due to scalability).

13. 

Repeat problem 12 for data partitioning.

14. 

Repeat problem 12 for spatial scalability.



Standard Codecs(c) Image Compression to Advanced Video Coding
Standard Codecs: Image Compression to Advanced Video Coding (IET Telecommunications Series)
ISBN: 0852967101
EAN: 2147483647
Year: 2005
Pages: 148
Authors: M. Ghanbari

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