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  1. 1. Multimedia System and Design Video
  2. 2. Overview • Using video. • How video works? • Broadcast video standards. • Analog video. • Digital video. • Video recording and tape formats. • Shooting and editing video. • Optimizing video files for CD-ROM.
  3. 3. Video • Video is the most recent addition to the elements of multimedia • It places the greatest demands on the computer and memory (using about 108 GB per hour for full motion) • Often requires additional hardware (video compression board, audio board, RAID - Redundant Array of Independent Disks- for high speed data transfer)
  4. 4. Using Video • Carefully planned video can enhance a presentation (eg. film clip of JFK, better than an text box of same message) • Before adding video to a project, it is essential to understand the medium, how to integrate it, its limitations, and its costs
  5. 5. Using Digital Video • Digital video has replaced analog as the method of choice for making and delivering video for multimedia. • Digital video device produces excellent finished products at a fraction of the cost of analog.
  6. 6. Using Digital Video • Digital video eliminates the image- degrading analog-to-digital conversion. • Many digital video sources exist, but getting the rights can be difficult, time-consuming, and expensive.
  7. 7. Video Clips • Ways to obtain video – shoot new film clips with a digital camcorder – convert you own video clips to digital format – acquire video from an archive - often very expensive, difficult to obtain permissions or licensing rights • Be sure to obtain permission from anyone you film or for any audio you use!
  8. 8. How Video Works • Light passes from an object through the video camera lens and is converted into an electrical signal by a CCD (charge-coupled device). • High quality cameras have 3 CCD. Each one take separate measurement of primary colors. • Signal contains 3 channels of color information (red, green, blue) and a synchronization pulse.
  9. 9. How Video Works • If each channel of a color signal is separate it is called RGB ( preferred) • A single composite of the colors and sync signal is less precise • A typical video tape has separate tracks for audio, video, and control
  10. 10. Video Basics
  11. 11. How Video Works • The video signal is magnetically written to tape by a spinning recording head following a helical path • Audio is recorded on a separate straight track • The control track regulates the speed and keeps the tracks aligned as the tape plays/records.
  12. 12. Video Basics
  13. 13. Broadcast Video Standards • NTSC • PAL • SECAM • HDTV  Six different formats  Aspect ratio is 16:9
  14. 14. Broadcast Video Standards National Television Standards Committee (NTSC): – These standards define a method for encoding information into electronic signal that creates a television picture. – It has screen resolution of 525 horizontal scan lines and a scan rate of 30 frames per second.
  15. 15. Broadcast Video Standards • NTSC- National Television Standards Committee - 1952, (“never the same color”) • 1 frame = 525 horizontal lines every 1/30 second (Electron Beam makes) • 2 passes - odd/even lines, 60/second (60 Hz) • Interlacing (Display single video frame in two halves)- to reduce flicker
  16. 16. Broadcast Video Standards Phase Alternate Line (PAL) and Sequential Color and Memory (SECAM): • PAL has a screen resolution of 625 horizontal lines and a scan rate of 25 frames per second. • SECAM has a screen resolution of 625 horizontal lines and is a 50 Hz system. • SECAM differs from NTSC and PAL color systems in its basic technology and broadcast method.
  17. 17. Broadcast Video Standards Advanced Television Systems Committee (ATSC) Digital Television (DTV): • This digital standard provides TV stations with sufficient bandwidth to present one High Definition TV (HDTV) signal. • This standard allows for transmission of data to computers and for new Advanced TV (ATV) interactive services. • Digital television (DTV)  is  the  transmission  of  audio  and  video  by  digitally  processed  and  multiplexed signal, in contrast to the totally analog  and  channel  separated  signals  used  by  analog television. Digital TV can  support  more  than one program in the same channel bandwidth.
  18. 18. Broadcast Video Standards • Several incompatible standards: • NTSC (US, Japan, many other countries) • PAL - (United Kingdom, parts of Europe, Australia, South Africa) • SECAM - (France Russia, few others) • HDTV - ( US ) - newest technology
  19. 19. Broadcast Video Standards • HDTV- High Definition Television now available, allow viewing of Cinemascope and Panavision movies with aspect ratio 16:9 ( wider than high) • Twice the resolution, interlaced format • Digitized then compressed for transmission
  20. 20. Broadcast Video Standards • 4: 3 Aspect Ratio
  21. 21. Broadcast Video Standards • 16: 9 Aspect Ratio
  22. 22. Summary: • NTSC uses a refresh rate of 60Hz while PAL and SECAM use 50Hz • NTSC has 525 lines while PAL and SECAM use 625 lines • NTSC requires a tint control while PAL and SECAM doesn’t. • NTSC and PAL use QAM while SECAM uses FM. • NTSC and PAL sends the red and blue colors together while SECAM sends them alternately.
  23. 23. Integrating Computers and Television • Television video is based on analog technology and international broadcast standards • Computer video is based on digital technology and other image display standards • DVD and HDTV merges the two
  24. 24. Analog Video – Analog television sets remain the most widely installed platforms for delivering and viewing video. – Television sets use composite input. Hence colors are less pure and less accurate than computers using RGB component. – NTSC television uses a limited color palette and restricted luminance (brightness) levels and black levels.
  25. 25. Analog Video – Some colors generated by a computer that display fine on a RGB monitor may be illegal for display on a NTSC TV. – While producing a multimedia project, consider whether it will be played on a RGB monitor or a conventional television set.
  26. 26. Video Overlay System • To display analog video (TV) images on a computer monitor, the signal must be converted from analog to digital form. • A special digitizing video overly board is required for the conversion • Produces excellent quality, full screen, full motion video, but costly.
  27. 27. Video Overlay System • Many companies use computer based training (CBT) systems • These require a computer and monitor cabled to a TV and video disc player. • Overlay boards allow the video disc to be controlled by the computer and display the images on the computer screen.
  28. 28. Video Capture Boards • Video overlay boards can capture or digitize video frames and play them back as QuickTime MPEG (Moving Picture Expert Group) and AVI movies. • Some also include audio input and sound management to interleave sound and images • Some also offer compression and accelerate digitizing, or support NTSC video.
  29. 29. Differences Between Computer and TV Video • Computer scan refresh rate = 480 lines/sec • Computer scan is progressive ( non- interlaced) at 66.67 HZ or higher • TV scans at 525 (or 625) lines/sec, with interlacing at a frame rate of 60 Hz
  30. 30. Interlacing Effects • Interlacing is a technique of improving the picture quality of a video signal primarily on CRT devices without consuming extra bandwidth. • On a computer (RGB) monitor, lines are painted one pixel thick and are not interlaced. Displayed on a TV they “flicker” because they appear in every other field. To avoid this avoid very thin lines and elaborate serifs.
  31. 31. Differences Between Computer and TV Video • TV broadcasts an image larger than the screen so that the “edge” of the image is against the edge of the screen. This is called overscan • Computer images are smaller than the screen area (called underscan) and there is a border around the image
  32. 32. Computers and Video
  33. 33. Differences Between Computer and TV Video • When a computer screen is converted to video the outer edges do not fit on the TV screen only about 360-480 lines of the computer image are visible. • Avoid using the outer 15% of the screen for graphics, or titles for use on TV • Use the safe title area.
  34. 34. Video Color • Color reproduction and display are also different in TV and computers monitors • Computers use RBG component video and produce more pure color • NTSC TV uses a limited color palette and restricted luminance (brightness) and black levels
  35. 35. Working with Text and Titles for Video Productions • Use plain, bold, easily read fonts • Use light color text on a dark background • Avoid color combinations like yellow/violet, blue/orange which “vibrate” • Avoid black or colored text on white background
  36. 36. Working with Text and Titles for Video Productions • Make lines and graphics at least two pixels wide • Use parallel lines and boxes sparingly and draw them with thick lines • Avoid “hot” colors • Keep graphics and titles in the safe screen area
  37. 37. Working with Text and Titles for Video Productions • Bring titles on slowly and let them remain on the screen sufficiently long. • Avoid “busy” screens- use additional pages instead
  38. 38. Digital Video • Digital video architecture. • Digital video compression.
  39. 39. Digital Video Architecture • Digital video architecture consists of a format for encoding and playing back video files by a computer. • Architecture includes a player that can recognize and play files created for that format.
  40. 40. Digital Video Compression • Digital video compression schemes or “codecs” ( coder/decoder) is the algorithm used to compress (code) a video for delivery. • The codec then decodes the compressed video in real-time for fast playback. • Streaming audio and video starts playback as soon as enough data has transferred to the user’s computer to sustain this playback.
  41. 41. Video Compression • To store even a 10 second movie clip requires the transfer of an enormous amount of data in a very short time • 30 seconds of video will fill a 1 GB hard drive • Typical hard drives transfer about 1MB/second and CD- ROMs about 600K/second
  42. 42. Video Compression • Full motion video requires the computer to deliver the data at 30 MB/second more than today’s PCs and MACs can handle • Solution- use video compression algorithms or codecs • Codecs compress the video for delivery and then decode it for playback at rates from 50:1 to 200:1
  43. 43. Video Compression & Streaming • Codecs ( such as MPEG, JPEG) use lossy compression schemes • Streaming technologies are also used to provide reasonable quality , low-bandwidth on the WEB • Playback starts as soon as enough data have been transferred to the user’s computer instead of waiting for the whole file to download • ( RealAudio and RealVideo software)
  44. 44. MPEG • Standard developed by the Moving PIcturesExperts Group for digital representation of moving pictures and associated audio • http://mpeg.org
  45. 45. Digital Video Compression • MPEG is a real-time video compression algorithm. (Moving Picture Experts Group) • MPEG-4 (1998-1999) includes numerous multimedia capabilities and is a preferred standard. • MPEG-7 (2002) (or Multimedia Content Description Interface) integrates information about motion video elements with their use. • MPEG –21 under development
  46. 46. Digital Video • Video clips can be shot or converted to digital format and stored on the hard drive. • They can be played back without overlay boards, second monitors or videodiscs using QuickTime or Active Movie for Windows • Analog video can be converted to digital or now created in digital form
  47. 47. Video Recording and Tape Formats • Composite analog video. • Component analog video. • Composite digital. • Component digital. • ATSC digital TV.
  48. 48. Composite Analog Video • Composite video combines the luminance and chroma information from the video signal. • Composite video produces lowest quality video and is most susceptible to generation loss. • Generation loss is the loss of quality that occurs while moving from original footage to editing master to copy.
  49. 49. Component Analog Video • Component video separates the luminance and chroma information. • It improves the quality of the video and decreases generation loss. • In S-video, color and luminance information are kept on two separate tracks (Y/C) to improve the picture quality. • Betacam is a new portable professional video format which lays the signal on the tape in three component channels.
  50. 50. Composite Digital • Composite digital recording formats combine the luminance and chroma information. • They sample the incoming waveforms and encode the information in binary (0/1) digital code. • It improves color and image resolution and eliminates generation loss.
  51. 51. Component Digital • Component digital formats add the advantages of component signals to digital recording. • D-1 component digital format is an uncompressed format which has a very high quality image. • It uses a 19 mm (3/4-inch) tape in order to save data. • Several other digital component formats are DCT, Digital Betacam, DV format, DVCPRO, and DVCAM formats.
  52. 52. ATSC Digital TV • These standards provide for digital STV and HDTV recordings that can be broadcast by digital TV transmitters to digital TV receivers. • ATSC standards also provide for enhanced TV bringing the interactivity of multimedia and the Web to broadcast television.
  53. 53. Vaughn’s Law of Multimedia Minimums • Your goal is to produce multimedia that is adequate and does it’s job but doesn’t throw you into bankruptcy. • Experiment with various levels of consumer grade equipment • Professional sound and video equipment is very expensive
  54. 54. Recording Formats • S-VHS and Hi-8 consumer quality • Component (YUV) - Sony BetacamSP the professional standard for broadcast quality • Component Digital- a digital version of the Betacam- best format for graphics > $900,000 and produces 15 minutes of video • Composite Digital most common >$110,000
  55. 55. Shooting and Editing Video • Shooting platform – use a steady tripod – or a camera with an electronic image stabilization feature to avoid “shaky hand effect” – or use camera moves and moving subjects to disguise your lack of steadiness
  56. 56. Shooting and Editing Video • Lighting performance is the main difference between professional and consumer camcorders • Use a simple floodlight kit or natural daylight to improve the image • Onboard flood lights can be used as fill light to illumine faces
  57. 57. Shooting and Editing Video
  58. 58. Shooting and Editing Video • Chroma Key or Blue Screen - popular technique for making multimedia without the use of expensive backgrounds • In shooting against a blue screen, be sure that the lighting is perfectly even and that actors are not too close to the screen so that color “spills” over on them
  59. 59. Shooting and Editing Video • Composition – Avoid wide panoramic shots – Use close-ups, head and shoulders – Remember the more a scene changes the slower the playback will be – Keep the camera still, let the subject add the motion by walking, turning...
  60. 60. Using Video Tapes • Fast forward new tapes and rewind them so that the tension is even (called “packing”) • Black-stripe the tape by running it through the recorder with the lens cap on -eliminates “snowy noise” • Do not reuse tapes after editing • Remove break off tab to avoid overwriting
  61. 61. Video Hardware Resolution • Horizontal resolution -the number of lines of detail the camera can reproduce • Different from the vertical scan lines on TV • The lens, and number, size and quality of the CCDs determine the resolution • Poor resolution = poor image
  62. 62. Consumer Grade Equipment • Mass production at low cost; easier to use • Cameras and camcorders that use HI-8 and S-VHS formats are superior to 8 mm and VHS systems • HI-8 is most widely available tape format and best consumer grade
  63. 63. Making Tape Copies • For demo or promo tapes use at least Super VHS ( HI-8 is best and allow unlimited copies to be made without degradation) • Copying ( dubbing) depends on the tape format and the quality of the equipment being used • Copy in SP mode- faster writing produces better images
  64. 64. Video Window Size • Shrinking a digitized image improves it perceived sharpness • ( Also happens when you switch from 19” to 13” TV) • The image is crisper because the scan lines are closer together
  65. 65. Editing with Consumer VCRs • Editing with 2 VCRs causes problems because the two machines are not in sync • Editing software, such as Premier, or After Effects, has become more commonly used in multimedia
  66. 66. P*64 • Video telephone conferencing standard for compressing audio and motion video images • Encodes audio and video for transmission over copper or fiber optic lines • Other compression systems are currently being developed by Kodak, Sony, etc.
  67. 67. Optimizing Video files for CD-ROMs • CD- ROMs are an excellent distribution media for multimedia: inexpensive, store great quantities of information, with adequate video transfer rates • Suitable for QuickTime and AVI file formats as well as those produced by Director, etc.
  68. 68. Optimizing Video files for CD-ROMs • Limit the synchronization between video and audio – AVI interleaves them – QuickTime files must be “flattened” - to interleave the audio and video • Use regularly spaced key frames (10 to 15 frames apart) • Limit the size of the video window- the more data the slower the playback
  69. 69. Optimizing Video files for CD-ROMs • Choose the software compression algorithm carefully – Sorenson codec is optimized for CD- ROM playback – Cinepack algorithm, available with AVI and QuickTime, is also optimized for CD-ROM playback – Use Norton speed Disk to defragment your files before burning the master
  70. 70. Summary • Various video standards are NTSC, PAL, SECAM, and ATSC DTV. • Categories of video standards are composite analog, component analog, composite digital, and component digital.

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