Chapter 20: Multimedia Systems

Chapter 20: Multimedia Systems

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Chapter 20: Multimedia Systems
„ What is Multimedia? „ Compression „ Requirements of Multimedia Kernels „ CPU Scheduling „ Disk Scheduling „ Network Management „ An Example: Cineblitz

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Objectives
„ To identify the characteristics of multimedia data „ To examine several algorithms used to compress multimedia data „ To explore the operating system requirements of multimedia data,
including CPU and disk scheduling and network management

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What is Multimedia?
„ Multimedia data includes - audio and video clips (i.e., MP3 and MPEG files) - live webcasts
„ Multimedia data may be delivered to - desktop PC’s - handheld devices (PDAs, smart phones

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Media Delivery
„ Multimedia data is stored in the file system like other ordinary data.
„ However, multimedia data must be accessed with specific timing requirements.
„ For example, video must be displayed at 24-30 frames per second. Multimedia video data must be delivered at a rate which guarantees 24-30 frames/second.
„ Continuous-media data is data with specific rate requirements.

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Streaming
„ Streaming is delivering a multimedia file from a server to a client typically the deliver occurs over a network connection
„ There are two different types of streaming: 1. Progressive download - the client begins playback of the multimedia file as it is delivered. The file is ultimately stored on the client computer 2. Real-time streaming - the multimedia file is delivered to - but not stored on - the client’s computer

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Real-time Streaming
„ There are two types of real-time streaming: 1. Live streaming - used to deliver a live event while it is occurring 2. On-demand streaming - used to deliver media streams such as movies, archived lectures, etc. The events are not delivered in real-time

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Multimedia Systems Characteristics
„ Multimedia files can be quite large „ Continuous media data may require very high data rates „ Multimedia applications may be sensitive to timing delays during
playback of the media

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Compression
„ Because of the size and rate requirements of multimedia systems, multimedia files are often compressed into a smaller form
„ MPEG Compression: 1. MPEG-1 - 352 X 240 @ 30 frames/second 2. MPEG-2 - Used for compressing DVD and high-definition television (HDTV) 3. MPEG-4 - Used to transmit audio, video, and graphics. Can be delivered over very slow connections (56 Kbps)

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Operating Systems Issues
„ The operating system must guarantee the specific data rate and timing requirements of continuous media.
„ Such requirements are known as Quality-of-Service (QoS) guarantees.

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