操作系统课件PPT第七章.ppt

Multimedia Chapter 7 Introduction to Multimedia (1) Video On Demand: (a) ADSL vs. (b) cable Introduction to Multimedia (2) Some data rates multimedia, high performance I/O devices Note: 1 Mbps = 106 bits/sec but 1 GB = 230 bytes Multimedia Files A movie may consist of several files Audio Encoding (1) Audio Waves Converted to Digital electrical voltage input binary number as output Audio Encoding (2) Error induced by finite sampling called quantization noise Examples of sampled sound telephone – pulse code modulation audio compact disks Video Encoding Scanning Pattern for NTSC Video and Television Video CompressionThe JPEG Standard (1) RGB input data and block preparation The JPEG Standard (2) One block of the Y matrix and the DCT coefficients The JPEG Standard (3) Computation of the quantized DCT coefficients The MPEG Standard (1) Order of quantized values when transmitted The MPEG Standard (2) MPEG-2 has three kinds of frame: I, P, B Intracoded frames Self-contained JPEG-encoded pictures Predictive frames Block-by-block difference with last frame Bi-directional frames Differences with last and next frame The MPEG Standard (3) Consecutive Video Frames Multimedia Process Scheduling Periodic processes displaying a movie Frame rates and processing requirements may be different for each movie Rate Monotonic Scheduling Used for processes which meet these conditions Each periodic process must complete within its period No process dependent on any other process Each process needs same CPU time each burst Any nonperiodic processes have no deadlines Process preemption occurs instantaneously, no overhead Earliest Deadline First Scheduling (1) Real Time Scheduling algorithms RMS EDF Earliest Deadline First Scheduling (2) Multimedia File System Paradigms Pull and Push Servers VCR Control Functions Rewind is simple set next frame to zero Fast forward/backward are trickier compression makes rapid motion complicated special file containg e.g. every 10th frame Near Video