1. Multimedia Concepts

2. Topics
Multimedia Basic Terms
Multimedia Compression/Decompression
Multimedia Protocols

3. Multimedia Definition
Basic Terms
Multimedia Definition
The term multimedia usually implies that at least one of text ( structured/unstructured, hypertext, etc), graphics (drawings), or image (discrete media) is associated with either audio or motion video information (continuous media).

4. Basic Terms Multimedia streaming
Multimedia streaming is the overlapping the playout of the data at the receiver with the transmission by the sender.
A video stream consists of a sequence of images or frames.
A frame consists of a grid of pixels.
(Table 1)
An audio stream consists of a sequence of audio samples.

5. Basic Terms Term Definition Pixel Frame Stream Session Presentation
Picture element
Two-dimensional grid of pixels
Sequence of frames over time
Synchronized set of streams
Set of multimedia sessions
Table 1. Hierarchy of multimedia content.

6. Basic Terms
The advantage of streaming is that it can enable easier access to multimedia resources.
Another possibility is the integration of video and audio with other web-based applications, such as chat and other real-time collaboration tools.

7. Basic Terms Streaming vs. downloading
What Is The Difference Between Downloading and Streaming?
When you download a video, you have to copy the
entire file to your hard disk before you can play it.

8. Basic Terms
When the video is streamed, there is a small wait as the stream 'buffers' but there is no need to save the file.
Streaming is the act of sending media files (audio and/or video) over the Internet from one computer to another computer so that the media plays as it is being delivered.

9. Basic Terms Multimedia Streaming Media Server Media Encoding Clients
Proprietary
Format
Multicast capable
More Robust
Access to Storage
Relieves Web Server
Send Stream
To Clients
Standalone player
Java based player
Browser plug-in player
Appliance
Decode
Buffer
Sync.
Media
Encoding
Audio
Video
Animation
Clients
Send Request
To Servers
Web
Server
Send Request to Media Server
Figure 2. To hear or view a media file without downloading it

10. Basic Terms
A media stream proceeds through the following stages before it is displayed to a recipient:
Capturing
The audio or video stream must be captured from an analog device, such as a microphone or a video camera, and converting to a digital form.
25 fps (frame per second) for video and 16-bit for audio is suitable.

11. Basic Terms Encoding Storing Delivering
An encoder converts the raw digital data into a particular audio or video format.
Storing
A server may store the encoded stream for future transmission.
Delivering
The stream is transmitted to one or more recipients. A live stream may be transmitted as it is captured and encoded, whereas a prerecorded stream is transmitted by a server.

12. Basic Terms
Decoding
The receiver decodes and displays the data as they arrive. Alternatively, the receiver may store the entire stream before initiating playback.
(Figure 3)

13. Basic Terms
Figure 3. Capturing Video

14. There are two different types of streaming:
Basic Terms
There are two different types of streaming:
Progressive download
The client begins playback of the multimedia file as it is delivered. The file is ultimately stored on the client computer.
Use standard web server
Quality is better than real-time streaming
Real-time streaming
The multimedia file is delivered to the client computer but the file is not stored on the client computer.
Require a special streaming server

15. two different types of real-time streaming:
Basic Terms
two different types of real-time streaming:
Live streaming
used to deliver a live event while it is occurring.
Examples: live soccer game, live concerts, live radio, and videoconferences.
On-demand streaming
used to deliver archived media streams.
Examples: video clips, movies, and
lectures.

16. Why Streaming Media? Basic Terms No waiting for complete downloads.
Streamed files are not written to disk.
Presentation of live events is possible.

17. Major streaming formats
Basic Terms
Major streaming formats
Microsoft Windows Media
Real Networks
Apple Quicktime

18. How does streaming work?
Basic Terms
How does streaming work?
Figure 4. Streaming media development process

19. How does streaming work?
Basic Terms
How does streaming work?
Figure 5. Streaming media playback

20. Basic Terms
Figure 6. Streaming media from a conventional Web server

21. Figure 7. Realtime Streaming protocol
Basic Terms
Figure 7. Realtime Streaming protocol

22. Basic Terms RTSP States
SETUP - the server allocates resources for a client session.
PLAY - the server delivers a stream to a client session.
PAUSE - the server suspends delivery of a stream.
TEARDOWN - the server breaks down the connection and releases the resources allocated for the session.

23. Figure 8. RTSP state machihne
Basic Terms
RTSP State Machine
Figure 8. RTSP state machihne

24. Basic Terms
RTSP operation

25. Basic Terms
Clip
Clip is a media file that contains audio, video, or both.

26. Basic Terms
Webcast
A webcast uses streaming media technology to take a single content source and distribute it to many simultaneous listeners/viewers by broadcasting over the Internet.

27. Basic Terms
Three general methods for delivering content from a server to a client across a network:
Unicasting
The server delivers the content to a single client. 
Broadcasting
The server delivers the content to all clients, regardless whether they want the content or not. 
Multicasting
The server delivers the content to a group of receivers who indicate they wish to receive the content.

28. Broadcasting Basic Terms
Broadcast means a piece of information is sent or transmitted from one point to all other points.
There is just one sender, but the information is simultaneously sent to all connected receivers.
In telecommunications, broadcasting means propagation of a flow of information from one source to all potential recipients.

29. Broadcasting Basic Terms
In networking, a distinction is made between broadcasting and multicasting.
Broadcasting sends a message to everyone
on the network.
Multicasting sends a message to a select list of recipients.

30. Figure 10. Unicast delivering
Basic Terms
Figure 10. Unicast delivering

31. Figure 11. Multicast delivering
Basic Terms
Figure 11. Multicast delivering

32. Figure 12. Unicast/Multicast delivering
Basic Terms
Unicast/Multicast
Host
Router
Unicast
Host
Router
Multicast
Figure 12. Unicast/Multicast delivering

33. Basic Terms Bit rate Multiple Bit Rate Encoding
Bit rate is amount of data that can be carried from one point to another in a given time period (usually a second).
Bit rate is sometimes called data rate or transfer rate or bandwidth.
Multiple Bit Rate Encoding
Combine several streams with different bit rate into a single file
The appropriate bit rate stream is automatically selected
(Figure 13)

34. Basic Terms
Figure 13. Multiple bit rate encoding

35. Basic Terms Aspect Ratio
This is the ratio of width to height that the encoded video will be.
This information is present in the output video stream and used by the decoder to display the video at the correct aspect ratio.
The computer display is designed for an aspect ratio of 1.33:1, which means that the width of the display area is only 1.33 times the height, almost square.

36. Basic Terms Frame Frame means one still picture.
By changing still pictures (frames) quickly, human eye "thinks" that the video is smooth and can't separate pictures from each others and instead sees smooth video.

37. Basic Terms
Frame rate
Frame rate is the number of video frames (complete pictures) that will be presented to the viewer each second.
Human eye can sees smooth video with the frame rate more than ~24 fps (frames per second).
In American TV system, NTSC, the frame rate is approximately fps.
In European PAL system the frame rate is 25fps.

38. Basic Terms Frame Buffer
Frame buffer is a special memory to hold the complete digital representation of the frame to be displayed on a computer screen.
The frame buffer is scanned line by line by the digital-to-analog converter system of the display.

39. Basic Terms Color depth
Color depth or bit depth is the number of bits used to represent the color of a single pixel in a bitmapped image or video frame buffer.
It is known as bits per pixel (bpp).
Higher color depth gives a broader range of distinct colors.
(Table 2)

40. 16,777,216 (True Color + Alpha Channel)
Basic Terms
Bit-Depth
Number of Colors 1
2 (monochrome) 2
4 (CGA) 4
16 (EGA) 8
256 (VGA) 16
65,536 (High Color, XGA) 24
16,777,216 (True Color, SVGA) 32
16,777,216 (True Color + Alpha Channel)
Table 2. Color depth chart.

41. Basic Terms
Jitter
In transmission technology, jitter refers to the variation of the delay generated by the transmission equipment.
In data communications, jitter refers to the variation over time of the network transit delay.

42. Multimedia Compression
Lossless compression
Lossy compression
Compression/Coding Standards
Decompression
Codec

43. Multimedia Compression
Compression is the process of eliminating redundant information to decrease file size.
Compression converts frames and pixels to mathematical algorithms that the computer can understand.
Decompression converts mathematical algorithms back to frames and pixels for playback.

44. Multimedia Compression
Two compression methods are:
Lossless compression
Run-Length coding
Huffman coding
Arithmetic coding
Lossy compression
Transform coding

45. Lossless compression
Lossless compression retains all of the data of the original file as it's converted to a smaller file size.
In lossless compression the information is recovered without any alteration after the decompression stage.
When a lossless file is opened, algorithms restore all compressed information, creating a duplicate of the source file.

46. Lossless compression
It generally preferred for creating high-quality or professional applications.
Lossless compression is applied where the accuracy of the information is essential, such as in medical imaging where it's important to retain fine detail.
Lossless compression is also called bit-preserving compression.

47. Lossy compression
Lossy compression refers to the case where the decompressed information is different from the original uncompressed information.
With this kind of compression, some of the source file's information is discarded to conserve space.

48. Lossy compression
When the file is decompressed, this information is reconstructed through algorithms.
This method results in some loss of sound quality or image detail when compared to the original.
This mode is suitable for most continuous media such as sound and motion video as well as for many images.

49. Compression/Coding Standards
The MPEG Standards
MPEG standards developed and managed by Motion Picture Experts Group (MPEG)
MPEG-1: VCD
MPEG-2: DVD, HDTV
MPEG-4: Content-based video coding
MPEG-7: Multimedia indexing and retrieval
MPEG-21: Multimedia delivery and consumption

50. Compression/Coding Standards
The MPEG-1
Released in 1992
A standard for coded representation of
Moving pictures
Audio
Combination of above
Typical application – video CD (VCD)

51. Compression/Coding Standards
The MPEG-2 Standard
Released in 1994
A standard to provide video quality not lower than NTSC/PAL with bit rates target between 2-10 Mbit/s
Applications
Digital cable TV distribution
Networked database service via ATM
Digital video tape recorder (VTR)
Satellite and terrestrial digital broadcasting distribution
It also supports HDTV applications, and so pre-emptied MPEG-3 standard

52. Compression/Coding Standards
The MPEG-4 Standard
First released in 1998, and targeted for content-based multimedia applications and low bit-rate video coding.
Algorithms and tools for coding and flexible representation of audio/video to meet the challenges of multimedia applications.
The objective of low bit-rate video coding was later accomplished by H.264, the convergence of ITU-T H.263 and MPEG-2.

53. Compression/Coding Standards
The MPEG-7
First release in 2001
Official name: Multimedia Content Description Interface
Objective:
To allow efficient search for multimedia content using standardized descriptors
The main research issues:
Optimum search engine
Feature analysis & query design

54. Compression/Coding Standards
The MPEG-21 Standard
Aim at defining a normative open framework for multimedia delivery and consumption for use by all the players in the delivery and consumption chain.

55. Decompression
Decompression is the process by which compressed information is expanded by addition of the redundant information eliminated at the compression stage.
After decompression, the resulting information may be identical to the original – lossless compression – or be different – lossy compression.

56. Codec
Codec stands for Coder/Decoder or Compression/Decompression.
Codec is a piece of software or a driver that is mostly for compression to reduce file size but may also do some formatting.
Compression is the primary function of the Codec.

57. Codec
With codec, your system recognizes the encoded video/audio format and allows you to play (decode) the audio/video file in a particular format.

58. Codec Examples Video Audio Image Data
MPEG1, MPEG2, DIVX, WMV(WINDOWS MEDIA VIDEO), MPEG4-H264, RealVideo
Audio
MP3,ATRAC, AAC, WMA (WINDOWS MEDIA AUDIO), DTS, RealAudio
Image
JPEG, JPEG2000, PNG, GIF
Data
ZIP, STUFFIT

59. Multimedia Protocols
TCP (Transmission Control Protocol)
UDP (User Datagram Protocol)
RTP (Real-time Transport Protocol)
RSVP (Resource ReSerVation Protocol)
(Table 3)

60. Multimedia Protocols Table 3. Multimedia protocols.
MULTIMEDIA CONCEPTS
Multimedia Protocols
Network Protocol
Advantage
Disadvantage
TCP
· Dominate protocol for data
transfer of data over the Internet
· Streaming through firewall
· Reliable
· Typically need large buffer to
handle data rate variation
· Loss recovery needs retransmission
causing further jitter or skew
· No support for multicast
UDP
· Suitable for streaming
· Allows packet drops; if packets
arrive late or damaged,
streaming will continue
· No retransmission needed
· Many network firewalls block
UDP data
· Need error concealment for video
packet loss
· No support for congestion control
· Cannot be played using popular
stream players such as QuickTime
RTP/RTCP
· Support real-time transmission
· Provide timing reconstruction,
loss detection, security and
content identification
· Allows retrieval of very
interesting network statistics
· No guarantee for QoS
· Header is larger than UDP
· More complicated that UDP
RSVP
· Reliable connection
· Receiver can obtain different
levels of service
· Complicated request mechanism
· Receivers may experience random
packet loss for small reservation
Table 3. Multimedia protocols.

61. References
B.Krishnamurthy, J. Rexford. “Web Protocols and Practice”, 2001
A.Silberschatz, P.Garvin, G.Gange. “ operating system concepts”, 2005
H.Sun, A Vetro, J. Xin. “ An Overview of Scalable Video Streaming”. 2007
Z.Li and M.S.Drew. “Fundamentals of Multimedia”, Prentice-Hall 2004
R.Steinmetz, K.Nahrstedt, “Multimedia: Computing, Communications and Applications”, Prentice-Hall 1995

62. References
T.Vaughan, “Multimedia: Making it Work, 7th Edition”, McGraw-Hill College 2006
L.Guan, S.Y.Kung, J.Larsen “Multimedia image and video processing”

63. References File Formats Image Compression
JPEG:
JPEG:
Video Compression
MPEG-4 pt. 2:
MPEG-4 pt. 10/H.264/AVC:
File Formats
General info:
Containers:
MPEG-4 pt. 14:
Codec list:
Audio
MP3:

64. References
DCT Basis Function Image: GNU licensed
JPEG Example Image: , by Ilmari Karonon at Wikipedia, Creative Commons Attribution-ShareAlike 2.5 License
MP3 File Image: