vdocument.in_modern-operating-systems-third-edition-andrew-s-tanenbaum-chapter-7-multimedia.ppt

MODERN OPERATING SYSTEMS
Third Edition
ANDREW S. TANENBAUM
Chapter 7
Multimedia Operating
Systems
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0-13-6006639

Figure 7-1. Video on demand using different
local distribution technologies. (a) ADSL.
Introduction To Multimedia (1)

Figure 7-1. Video on demand using different
local distribution technologies. (b) Cable TV.

Key characteristics of multimedia:
1. Multimedia uses extremely high data
rates.
2. Multimedia requires real-time playback.

Figure 7-2. Some data rates for multimedia and high-performance
I/O devices. Note that 1 Mbps is 106 bits/sec
but 1 GB is 230 bytes.

Figure 7-3. A movie may consist of several files.
Multimedia Files

Figure 7-4. The scanning pattern used for NTSC
video and television.
Video Encoding

Figure 7-5. (a) A sine wave. (b) Sampling the sine wave.
(c) Quantizing the samples to 4 bits.
Audio Encoding

Figure 7-6. (a) RGB input data. (b) After block preparation.
The JPEG Standard (1)

Figure 7-7. (a) One block of the Y matrix.
(b) The DCT coefficients.

Figure 7-8. Computation of the quantized DCT coefficients.

Figure 7-9. The order in which the quantized
values are transmitted.

The MPEG Standard (1)
Three types of MPEG-2 frames processed
by the viewing program:
1. I (Intracoded) frames: Self-contained
JPEG-encoded still pictures.
2. P (Predictive) frames: Block-by-block
difference with the last frame.
3. B (Bidirectional) frames: Differences with
the last and next frame.

Figure 7-10. Three consecutive video frames.
The MPEG Standard (2)

Figure 7-11. (a) A binary signal and its
root-mean-square Fourier amplitudes.
Audio Compression (1)

Figure 7-11. (b)–(e) Successive approximations
to the original signal.

Figure 7-12. (a) The threshold of audibility as a
function of frequency. (b) The masking effect.

Possible sampling configurations:
1. Monophonic (a single input stream).
2. Dual monophonic (e.g., an English and a
Japanese soundtrack).
3. Disjoint stereo (each channel compressed
separately).
4. Joint stereo (interchannel redundancy fully
exploited).

Figure 7-13. Three periodic processes, each displaying a movie.
The frame rates and processing requirements per frame are
different for each movie.
General Real-Time Scheduling

Rate Monotonic Scheduling (1)
Required conditions for RMS:
1. Each periodic process must complete within its
period.
2. No process is dependent on any other
process.
3. Each process needs same amount of CPU
time on each burst.
4. Nonperiodic processes have no deadlines.
5. Process preemption occurs instantaneously
and with no overhead.

Figure 7-14. An example of RMS and EDF real-time scheduling.
Rate Monotonic Scheduling (2)

Figure 7-15. Another example of real-time
scheduling with RMS and EDF.
Earliest Deadline First Scheduling

Figure 7-16. (a) A pull server. (b) A push server.
Multimedia File System Paradigms

Figure 7-17. Near video on demand has a new stream
starting at regular intervals, in this example
every 5 minutes (9000 frames).
Near Video on Demand

Figure 7-18. (a) Initial situation. (b) After a rewind to 12 min
Near Video on Demand with VCR
Functions (1)

Figure 7-18. (c) After waiting 3 min.
(d) After starting to refill the buffer. (e) Buffer full.
Near Video on Demand with VCR
Functions (2)

Figure 7-19. Interleaving video, audio, and text in a single
contiguous file per movie.
Placing a File on a Single Disk

Figure 7-20. Noncontiguous
movie storage. (a) Small
disk blocks.
Two Alternative File
Organization
Strategies (1)

Figure 7-20.
Noncontiguous
movie storage
(b) Large disk
blocks.
Two Alternative File
Organization
Strategies (2)

Two Alternative File Organization
Strategies (3)
Trade-offs involved in these alternatives:
1. Frame index: Heavier RAM usage while movie
is playing; little disk wastage.
2. Block index (no splitting frames over blocks):
Low RAM usage; major disk wastage.
3. Block index (splitting frames over blocks is
allowed): Low RAM usage; no disk wastage;
extra seeks.

Figure 7-21. Optimal frame placement for near video on demand.
Placing Files for Near Video
on Demand

Figure 7-22. The curve gives Zipf’s law for N = 20. The
squares represent the populations of the 20
largest cities in the U.S., sorted on rank order
(New York is 1, Los Angeles is 2, Chicago is 3, etc.).
Placing Multiple
Files on a Single
Disk (1)

Figure 7-23. The organ-pipe distribution of files on a video server.
Placing Multiple Files
on a Single Disk (2)

Figure 7-24. Four ways of organizing multimedia files over
multiple disks. (a) No striping. (b) Same striping all files.
Placing Files on Multiple Disks (1)

Figure 7-24. Four ways of organizing multimedia files over
multiple disks. (c) Staggered striping. (d) Random striping.
Placing Files on Multiple Disks (2)

Figure 7-25. (a) Two users watching the same
movie 10 sec out of sync.
Block Caching (1)

Figure 7-25. (b) Merging the two streams into one.
Block Caching (2)

Figure 7-26. In one round, each movie asks for one frame.
Static Disk Scheduling

Figure 7-27. The scan-EDF algorithm uses deadlines and cylinder
numbers for scheduling.
Dynamic Disk Scheduling

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