Multimedia Systems：多媒体系统.pptVIP

Multimedia Systems CS-502 Operating Systems Outline Requirements and challenges for audio and video in computer systems Systems for multimedia Compression and bandwidth Processor scheduling File, disk, and network management Tanenbaum, Chapter 7Silbershatz, Chapter 20 What do we mean by “multimedia” Audio and video within a computer system CD’s DVD’s Computer hard drive Live broadcast web casts Webcams, Skype, … Video on demand Pause, fast forward, reverse, etc. Interactive meetings Presentations with 2-way audio Teleconferencing Interactive gaming … Requirements “Smooth” audio and video Deterioration in quality jerky playback Note: human is more sensitive to jitter in audio 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 System and OS Challenges Bandwidths and Compression Jitter Processor Scheduling Disk Scheduling Network Streaming Some System Architectures Simple: Data paths for audio/video that are separate from computational data paths Modern Fast system bus, CPU, devices Video server Disk farm and multiple streams System Organization (simple) Separate data path for audio stream Main system bus and CPU were too busy/slow to handle real-time audio System Organization (typical Pentium) Video Server Multiple CPUs Disk farm 1000s of disks Multiple high-bandwidth network links Cable TV Video on demand Internet 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 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 Why Compression? – Video “Standard” TV frame = 640 ? 480 pixels @ 25-30 frames/sec (fps) ? 9,216,000 pixels/sec = 27,648,000 bytes/sec HDTV = 1280 ? 720 pixels @ 30 fps 82,944,000 bytes/sec Typical movie ? 133 minutes approx. 220