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Multimedia

Multimedia. Week 4 LBSC 690 Information Technology. Agenda. Questions Muddiest Points XML Images Audio Transmission Project teams. Muddiest Points. Using other people’s pages Using FTP to get a Web page someplace Internal anchors Structure vs. appearance.

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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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