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Multimedia

Explore the fundamentals of XML, including structure, appearance, and behavior, as well as its role in multimedia content. Learn about key concepts, such as DTD, XLink, XSL, and examples of XML applications. Uncover the history of structured documents and how XML aims to unify various markup languages.

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Multimedia

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  1. Multimedia Week 4 LBSC 690 Information Technology

  2. Agenda • Questions • Muddiest Points • XML • Images • Audio • Transmission • Project teams

  3. Muddiest Points • Using other people’s pages • Using FTP to get a Web page someplace • Internal anchors • Structure vs. appearance

  4. What’s Wrong with the Web? • HTML • Confounds structure and appearance (XML) • HTTP • Can’t recognize related transactions (Cookies) • URL • Links breaks when you move a file (PURL)

  5. Discussion Point: Describing the Structure of Text • Entities • Span • Type/Attributes • Relationships • Part-whole • Is-a

  6. What’s a Document? • Content • Structure • Appearance • Behavior

  7. History of Structured Documents • Early standards were “typesetting languages” • NROFF, TeX, LaTeX, SGML • HTML was developed for the Web • Too specialized for other uses • Specialized standards met other needs • Change tracking in Word, annotating manuscripts, … • XML seeks to unify these threads • One standard format for printing, viewing, processing

  8. Goals of XML • Meta language • A toolkit for design markup languages • Unambiguous markup • Clear span of tags • Separate markup from presentation • Style info => stylesheet, so easy to change • Be simple

  9. A Family of Standards • Definition: DTD • Names known types of entities with “labels” • Defines part-whole and is-a relationships • Markup: XML • “Tags” regions of text with labels • Markup: XLink • Defines “hypertext” (and other) link relationships • Presentation: XSL • Specifies how each type of entity should be “rendered”

  10. XML Example • View “The Song of the Wandering Aengus” • http://glue.umd.edu/~rba/COURSES/TECHNOLOGY/XML/DTD/ • Built from three files • yeats01.xml • poem01.dtd • poem01.xsl

  11. An XML Example <?xml version="1.0"?> <!DOCTYPE POEM SYSTEM "poem01.dtd"> <?xml-stylesheet type="text/xsl" href="poem01.xsl"?> <POEM> <TITLE>The Song of Wandering Aengus</TITLE> <AUTHOR> <FIRSTNAME>W.B.</FIRSTNAME> <LASTNAME>Yeats</LASTNAME> </AUTHOR> <STANZA> <LINE>I went on to the hazel wood,</LINE> <LINEIN>Because a fire was in my head,</LINEIN> <LINE>And cut and peeled a hazel wand,</LINE> </STANZA> </POEM>

  12. Document Type Definition (DTD) <!ELEMENT poem ( (title, author, stanza)* )> <!ELEMENT title (#PCDATA) > <!ELEMENT author (firstname, lastname) > <!ELEMENT firstname (#PCDATA) > <!ELEMENT lastname (#PCDATA) > <!ELEMENT stanza (line+ | linein+) > <!ELEMENT line (#PCDATA) > <!ELEMENT linein (#PCDATA) > #PCDATA span of text a,ba followed by b a|b either a or b a* 0 or more a’s a+ 1 or more a’s

  13. Specifying Appearance: XSL <xsl:template match="POEM"> <HTML> <BODY BGCOLOR="#FFFFCC"> <xsl:apply-templates/> </BODY> </HTML> </xsl:template> <xsl:template match="TITLE"> <H1> <FONT COLOR="Green"> <xsl:value-of/> </FONT> </H1> </xsl:template>

  14. An XLink Example …… <poem xmlns:xlink="http://www.w3.org/1999/xlink"> <author xlink:href="yeatsRDFS3.xml“ xlink:type="simple">W. B. Yeats</author> <poems> <poem1 xlink:href="http://www.geocities.com/Athens/5379/yeats_index.html" xlink:type="simple">The Rose</poem1> <poem2 xlink:href="http://www.geocities.com/Athens/5379/yeats_index.html" xlink:type="simple">The Tower</poem2> </poems> </poem> ……….

  15. Some XML Applications • Text Encoding Initiative • For adding annotation to historical manuscripts • http://www.tei-c.org/ • Encoded Archival Description • To enhance automated processing of finding aids • http://www.loc.gov/ead/ • Metadata Encoding and Transmission Standard • Bundles descriptive and administrative metadata • http://www.loc.gov/standards/mets/

  16. What’s Wrong with the Web? • HTML • Confounds structure and appearance (XML) • HTTP • Can’t recognize related transactions (Cookies) • URL • Links breaks when you move a file (PURL)

  17. Cookies • Servers know users by IP address and port • Because that’s where they send the Web pages • Cookies preserve “state” • Server sends data to the browser • Browser later responds with the same data • A unique code (server-side state) • Information about the user (client-side state)

  18. Uniform Resource Names (URN) • Persistent URLs (www.purl.org) • http://purl.oclc.org/OCLC/PURL/FAQ/ My Browser PURL PURL Sever URL URL Resource Sever Page

  19. Summary • Learning to build simple Web pages is easy • Which is good news for the homework! • All documents are structured documents • XML is a flexible markup language toolkits • The key is to understand its capabilities • XML editors can hide much of the complexity

  20. Visual Perception • Closely spaced dots appear solid • But irregularities in diagonal lines can stand out • Any color can be produced from just three • Red, Blue and Green: “additive” primary colors • High frame rates produce apparent motion • Smooth motion requires about 24 frames/sec • Visual acuity varies markedly across features • Discontinuities easily seen, absolutes less crucial

  21. Basic Image Coding • Raster of picture elements (pixels) • Each pixel has a “color” • Binary - black/white (1 bit) • Grayscale (8 bits) • Color (3 colors, 8 bits each) • Red, green, blue • Screen • A 1024x768 image requires 2.4 MB • So a picture is worth 400,000 words!

  22. Monitor Characteristics • Technology (CRT, Flat panel) • Size (15, 17, 19, 21 inch) • Measured diagonally • For CRT, key figure is “viewable area” • Resolution • 640x480, 800x600, 1024x768, 1280x1024 pixels • Layout (three dot, lines) • Dot pitch (0.26, 0.28) • Refresh rate (60, 72, 80 Hz)

  23. Some Questions • How many images can a 64 MB flash card store? • But mine holds 120. How? • How long will it take to send an image at 64kb/s? • But my Web page loads faster than that. How? • But in reality images don’t have these problems • How do we get around these problems?

  24. Compression • Goal: reduce redundancy • Send the same information using fewer bits • Originally developed for fax transmission • Send high quality documents in short calls • Two basic strategies: • Lossless: can reconstruct exactly • Lossy: can’t reconstruct, but looks the same

  25. Palette Selection • Opportunity: • No picture uses all 16 million colors • Human eye does not see small differences • Approach: • Select a palette of 256 colors • Indicate which palette entry to use for each pixel • Look up each color in the palette … …

  26. Run-Length Encoding • Opportunity: • Large regions of a single color are common • Approach: • Record # of consecutive pixels for each color • An example of lossless encoding

  27. GIF • Palette selection, then lossless compression • Opportunity: • Common colors are sent more often • Approach: • Use fewer bits to represent common colors • 1 Blue 75% 75x1= 75 75x2=150 • 01 White 20% 20x2= 40 20x2= 40 • 001 Red 5% 5x3= 15 5x2= 10 130 200

  28. JPEG • Opportunity: • Eye sees sharp lines better than subtle shading • Approach: • Retain detail only for the most important parts • Accomplished with Discrete Cosine Transform • Allows user-selectable fidelity • Results: • Typical compression 20:1

  29. Variable Compression in JPEG 37 kB (20%) 4 kB (95%)

  30. Discussion Point: JPEG vs GIF in Web images • Which format should I use for images in my web pages? • Photos • text images • drawings

  31. Hands on Point: Convert between formats • Load and save two images • http://www.umiacs.umd.edu/~daqingd/image1.jpg • http://www.umiacs.umd.edu/~daqingd/image2.gif • Download the two images, use MS photo editor convert each to the other format, and compare the quality and the size. • Increase the compression rate for image1.jpg, and compare the quality

  32. Discussion Point: When is Lossless Compression Important? • For images? • For text? • For sound? • For video?

  33. Basic Video Coding • Display a sequence of images • Fast enough for smooth motion and no flicker • NTSC Video • 60 “interlaced” half-frames/sec, 512x486 • HDTV • 30 “progressive” full-frames/sec, 1280x720

  34. Video Compression • Opportunity: • One frame looks very much like the next • Approach: • Record only the pixels that change • Standards: • MPEG-1: Web video (file download) • MPEG-2: HDTV and DVD • MPEG-4: Web video (streaming)

  35. Basic Audio Coding • Sample at twice the highest frequency • One or two bytes per sample • Speech (0-4 kHz) requires 8 kB/s • Standard telephone channel (1-byte samples) • Music (0-22kHz) requires 88 kB/s • Standard for CD-quality audio (2-byte samples)

  36. Speech Compression • Opportunity: • Human voices vary in predictable ways • Approach: • Predict what’s next, then send only any corrections • Standards: • Real audio can code speech in 6.5 kb/sec • Demo at http://www.data-compression.com/speech.html

  37. Music Compression • Opportunity: • The human ear cannot hear all frequencies at once • Approach: • Don’t represent “masked” frequencies • Standard: MPEG-1 Layer 3 (.mp3)

  38. Transmission • Download • Transfer the whole file, then start replay • Can be very slow for large files • Streaming • Play the file as it is received • Also suitable for live broadcasts • Requires a sufficiently fast connection

  39. The “Last Mile” • Traditional modems • “56” kb/sec modems really move ~3 kB/sec • Digital Subscriber Lines • 384 kb/sec downloads (~38 kB/sec) • 128 kb/sec uploads (~12 kB/sec) • Cable modems • 10 Mb/sec downloads (~1 MB/sec) • 256 kb/sec uploads (~25kB/sec)

  40. Streaming Audio and Video • Buffering a portion of audio/video • Playing along with receiving • Interrupted when Rebuffering. Media Sever Buffer Internet

  41. Hands On: RealPlayer • View streaming real video at http://www.glue.umd.edu/~oard/teaching/690/fall03/syllabus.html • Pay attention to buffering • Look at the dropped packet statistics and the bandwidth monitor • Go to “Tools/playback statistics”

  42. Project • Teams of 3 • Best if you have complementary skills • Solve a real problem • Choose the standard one, or invent your own • Must integrate at least two technologies • Web, database, streaming media, programming

  43. The Apollo Archives • Text • Transcripts, press releases, manuals, flight plans, reports, books, oral histories • Video • Launch, movie film, television, splashdown • Audio • Radio, onboard recordings, interviews, press conferences • Images • Preflight, launch, onboard, splashdown, postflight http://www.hq.nasa.gov/alsj

  44. Possible User Groups • Museum visitors, in person • General public, over the Web • Children, on CDROM in school • Historians, with a search system

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