Multimedia Systems：多媒体系统

memory bus
Device
audio stream
CD-ROM drive
Sound card
• Separate data path for audio stream
• Main system bus and CPU were too busy/slow to handle real-time audio
– Okay for a modern PC – Not okay for 56 kb/sec modem (speed) or iPod (space)!
• MP-3 0.14 mbits/sec (10:1)
– Same audio quality! – Compression ratio varies with type of music
Multimedia Systems
CS-502 Operating Systems
CS502 Spring 2006
Multimedia Systems 1
Outline
• Requirements and challenges for audio and video in computer systems
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Multimedia Systems 7
System Organization (typical Pentium)
Level 2
cache
CPU
PCI bus
Ethernet
SCSI
USB
Mouse
Keyboard
CS502 Spring 2006
Main Memory
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Multimedia Systems 3
Requirements
• “Smooth” audio and video
– Deterioration in quality >> jerky playback – Note: human is more sensitive to jitter in audio
CS502 Spring 2006
Multimedia Systems 2
What do we mean by “multimedia”
• Audio and video within a computer system
– CD’s & DVD’s – Computer hard drive
• Live broadcast & web casts
• Systems for multimedia • Compression and bandwidth • Processor scheduling • File, disk, and network management
Tanenbaum, Chapter 7 Silbershatz, Chapter 20
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Multimedia Systems 9
Why Compression? – CD-quality audio
• 22,050 Hz 44,100 samples/sec
• 16 bits per sample
• Two channels 176,000 bytes/sec 1.4 mbits/sec
Multimedia Systems 8
Printer
Video Server
• Multiple CPUs • Disk farm
– 1000s of disks
• Multiple high-bandwidth network links
– Cable TV – Video on demand – Internet
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Multimedia Systems 10
Why Compression? – Video
• “Standard” TV frame = 640 480 pixels @ 25-30 frames/sec (fps)
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Multimedia Systems 5
Some System Architectures
• Simple:
– Data paths for audio/video that are separate from computational data paths
• Modern
video stream via ISA & bridge to
graphics card
AGP Port
Bridge
Graphics card
MonitorLeabharlann Baidu
ISA bridge
ISA bus
IDE disk
audio stream via ISA bridge to
sound card
Modem
Sound card
– Webcams, Skype, …
• Video on demand
– Pause, fast forward, reverse, etc.
• Interactive meetings
– Presentations with 2-way audio – Teleconferencing
• Interactive gaming •…
– Fast system bus, CPU, devices
• Video server
– Disk farm and multiple streams
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Multimedia Systems 6
System Organization (simple)
Memory
CPU
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Multimedia Systems 4
System and OS Challenges
• Bandwidths and Compression
• Jitter
• Processor Scheduling
• Disk Scheduling
• Network Streaming
than to jitter in video!
• Audio/video on PC’s doing something else • Multiple concurrent streams
– Video & multimedia servers – TiVo, etc.
• Wide range of network bandwidths