Multimedia Concepts

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Multimedia Concepts
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Topics
Multimedia Basic Terms Multimedia Compression/Decompression Multimedia Protocols
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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).
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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.
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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.
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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.
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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.
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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.
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Basic Terms
Multimedia Streaming
Figure 2. To hear or view a media file without
downloading it
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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.
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Basic Terms
Encoding 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.
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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)
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Basic Terms

Figure 3. Capturing Video
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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
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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.
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Basic Terms
Why Streaming Media? No waiting for complete downloads. Streamed files are not written to disk. Presentation of live events is possible.
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Basic Terms
Major streaming formats Microsoft Windows Media Real Networks Apple Quicktime
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Basic Terms
How does streaming work?
Figure 4. Streaming media development process
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Basic Terms
How does streaming work?
Figure 5. Streaming media playback
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Basic Terms

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

Figure 7. Realtime Streaming protocol
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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.
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Basic Terms
RTSP State Machine
Figure 8. RTSP state machihne
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Basic Terms
RTSP operation
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Basic Terms
Clip Clip is a media file that contains audio, video, or both.
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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.
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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.
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Basic Terms
Broadcasting 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.
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Basic Terms
Broadcasting 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.
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Basic Terms

Figure 10. Unicast delivering
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Basic Terms

Figure 11. Multicast delivering
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Basic Terms
Unicast/Multicast
Figure 12. Unicast/Multicast delivering
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Basic Terms
Bit rate 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)
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Basic Terms

Figure 13. Multiple bit rate encoding
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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 1.331, which means that the width of the display area is only 1.33 times the height, almost square.
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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.
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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 29.97 fps. In European PAL system the frame rate is 25fps.
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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.
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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)
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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.
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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.
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Multimedia Compression
Lossless compression Lossy compression Compression/Coding Standards Decompression Codec
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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.
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Multimedia Compression
Two compression methods are Lossless compression Run-Length coding Huffman coding Arithmetic coding Lossy compression Transform coding
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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.
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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.
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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.
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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.
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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
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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)
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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
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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.
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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
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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.
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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.
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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.
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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.
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Codec Examples
Video 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
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Multimedia Protocols
TCP (Transmission Control Protocol) UDP (User Datagram Protocol) RTP (Real-time Transport Protocol) RSVP (Resource ReSerVation Protocol) (Table 3)
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Multimedia Protocols
MULTIMEDIA CONCEPTS

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 No support for congestion control
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.
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References
B.Krishnamurthy, J. Rexford. Web Protocols and Practice, 2001 A.Silberschatz, P.Garvin, G.Gange. operating system concepts, 2005 http//www.micc.unifi.it/delbimbo/documents/prog_prod_multimediale/2 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
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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
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References
Image Compression JPEG http//www.faqs.org/faqs/jpeg-faq/part1/ JPEG http//en.wikipedia.org/wiki/JPEG Video Compression MPEG-4 pt. 2 http//en.wikipedia.org/wiki/MPEG-4_Part_2 MPEG-4 pt. 10/H.264/AVC http//en.wikipedia.org/wiki/H.264/MPEG-4_AVC File Formats General info http//en.wikipedia.org/wiki/File_format Containers http//en.wikipedia.org/wiki/Container_format MPEG-4 pt. 14 http//en.wikipedia.org/wiki/.m4a Codec list http//www.fourcc.org/ Audio MP3 http//en.wikipedia.org/wiki/MP3
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References
DCT Basis Function Image http//en.wikipedia.org/wiki/ImageDctjpeg.png, GNU licensed JPEG Example Image http//en.wikipedia.org/wiki/ImagePhalaenopsis_JPEG.jpg , by Ilmari Karonon at Wikipedia, Creative Commons Attribution-ShareAlike 2.5 License MP3 File Image http//en.wikipedia.org/wiki/ImageMp3filestructure.jpg