MEDIA APPLICATIONS DESIGN AND QUALITY OF EXPERIENCE (QOE)
(LLP105)
Question 1
Consider an Adaptive Bit-Rate (ABR) Streaming application. Answer the following questions accordingly.
i) What makes adaptive bit-rate streaming different from constant bit-rate streaming? Briefly describe their difference in terms of multimedia content preparation. [5 marks]
ii) Define the ABR application’s start-up delay. Why is this initial buffering part of the application design? [5 marks]
iii) In the adaptive streaming, the multimedia content is divided into successive temporal segments of certain length, such as 2 second, 5 second, or 10 second. Each segment is encoded at different bit-rates resulting in different qualities and stored in the server. They are requested by the client one after the other during a streaming session for download. Explain how the quality switches happen from time to time during streaming. What is the triggering factor? [5 marks]
iv) Now consider two different design choices. In one design choice, the segment size is fixed to 2 second (i.e., each temporal segment represents a 2 second long video). In the other design choice, the segment size is set to 10 second.
Briefly compare the two design choices in terms of (a) adaptation speed against network fluctuations, and (b) video compression performance.
(Hint: remember that each segment can be decoded on its own, which means that each segment starts with an Intra-coded frame. followed by Predictive-coded frames. Intra-coded frames are larger in size compared to Predictive-coded frames.) [10 marks]
Question 2
i) Briefly explain the Unicast, Multicast, and Broadcast transmission methods, which are utilised for multimedia transmission over the communication networks. Also give an example application scenario for each method. [9 marks]
ii) What are the four packet-level Quality of Service (QoS) parameters? [8 marks]
iii) Consider the following classes of applications, which differ in terms of QoS requirements:
(a) Conversational, (b) Streaming Media, (c) Interactive applications, and (d) Background applications. Qualitatively compare these four classes in terms of their different QoS requirements, by also giving some examples to each class. [8 marks]
Question 3
i) Briefly define the Mean Opinion Score (MOS) metric in quality measurement. What is its main advantage? Also discuss the difficulties in obtaining MOS results. [8 marks]
ii) Definition: Quality of Experience (QoE) is a quantified measure of the performance of a system as experienced by an end user, such as excellent, good, fair or bad. Quality of Service (QoS) is a quantified measure of several transmission medium related components, such as delay, jitter...
Why is it important for network service providers to define a link between the QoE and QoS (you can use an example)? [9 marks]
iii) Consider the following types of problems that can be observed in an audio-visual service:
(1) video blockiness, (2) video freeze, (3) audio synchronisation (or lip-sync), (4) video jerkiness.
Briefly discuss on the possible sources of these four problems, such as the content production side, the network transmission side, and the consumer display device side. [8 marks]
Question 4
i) Define gesture recognition by giving some examples. Comment on its role in user interaction with the multimedia applications. [10 marks]
ii) What is the difference between the Virtual Reality technology and the Augmented Reality technology? [5 marks]
iii) Consider an online video gaming system with two remote players (i.e., they are in different parts of the world). Each player has a game console with several input modalities, such as camera and depth sensors. The online gaming platform. captures each player’s input by analysing the hand and body gestures, and transmitting their commands over the network.
Discuss the implications of two players from different parts of the world playing the game from their homes, differentiating this situation against two players playing the game together in the same room. [10 marks]