Karen Fraser, 16G06

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Karen Fraser, 16G06

• email, k.fraser_at_ulster.ac.uk, website,
  karenfraser.co.uk

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Video Digital Multimedia, 2nd editionNigel
Chapman Jenny ChapmanEXAMPLE OF FLIP BOOK
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Data Size

• Either
• Actual motion
• Or
• Create single frames

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Data Size

• PAL uncompressed
• 768x576 pixels per frame
• x 3 bytes per pixel (24 bit colour)
• x 25 frames per second
• 31 MB per second
• 1.85 GB per minute

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Data Size

• NTSC uncompressed
• 640x480 pixels per frame
• x 3 bytes per pixel (24 bit colour)
• x 30 frames per second (approx)
• 26 MB per second
• 1.6 GB per minute

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Digitization

• In the camera DV Firewire
• In the computer video capture card
• Digitization in camera (DV) means less noise
• Less noise allows better compression

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Streamed Video

• Play back a video stream as it arrives over a
  network (like broadcast TV), instead of
  downloading an entire video clip and playing it
  from disk (like renting a DVD)

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HTTP Streaming

• Start playing a downloaded clip as soon as enough
  of it has arrived
• Starts when the (estimated) time to download the
  rest is equal to the duration of the clip

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HTTP Streaming
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BBC iPlayer

• Is a new multimedia tool
• It is a BBC interactive media player
• Delivers TV programme broadcast over the previous
  7 days
• Does not involve streaming
• Distribution is peer to peer

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Video Standards

• Digital video devices must conform to standards
• Digital standards must maintain compatibility
  with older analogue standards for broadcast TV

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PAL/ NTSC - Analogue

• Pal
• Frame has 625 lines, 576 are picture
• 25 frames (50 fields) per second
• NTSC
• Frame has 525 lines, 480 are picture
• 29.97 frames (59.94 fields) per second
• (Often quoted as 30 frames per second)

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MPEG

• ISO/IEC Motion Picture Experts Group
• Series of standards including
• MPEG-1 intended for video CD
• MPEG-2 used in DVD and broadcast
• MPEG-4 for low bitrate multimedia

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Editing

• Making a constructed whole from a collection of
  parts
• Selection, trimming and organization of raw
  footage
• Apply transitions (e.g. dissolves) between shots
• Combination of picture with sound
• No changes made to the footage itself

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Post-Production

• Changing or adding to the material
• Most changes are generalizations of image
  manipulation operations (e.g. colour correction,
  blurring and sharpening,)
• Compositing combining elements from different
  shots into a composite sequence
• Animating elements and combining animation with
  live action

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Preparing for Delivery

• Compromises required to bring resource
  requirements of video within capabilities of
  delivery media (e.g. networks) and low-end
  machines
• Reduce frame size (e.g. downsample to quarter
  frame)
• Reduce frame rate (12fps is OK for smooth motion,
  flicker not a problem on computer)
• Reduce colour depth

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Sound

• Digital Multimedia, 2nd edition
• Nigel Chapman Jenny Chapman
• Chapter 9

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The Nature of Sound

• Conversion of energy into vibrations in the air
  (or some other elastic medium)
• Most sound sources vibrate in complex ways
  leading to sounds with components at several
  different frequencies
• Frequency spectrum relative amplitudes of the
  frequency components
• Range of human hearing roughly 20Hz20kHz,
  falling off with age

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Waveforms

• Sounds change over time
• e.g. musical note has attack and decay, speech
  changes constantly
• Frequency spectrum alters as sound changes
• Waveform is a plot of amplitude against time
• Provides a graphical view of characteristics of a
  changing sound
• Can identify syllables of speech, rhythm of
  music, quiet and loud passages, etc

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Digitization Sampling

• Sampling Theorem implies minimum rate of 40kHz to
  reproduce sound up to limit of hearing
• CD 44.1kHz
• Sub-multiples often used for low bandwidth e.g.
  22.05kHz for Internet audio
• DAT 48kHz
• (Hence mixing sounds from CD and DAT will require
  some resampling, best avoided)

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Data Size

• Sampling rate r is the number of samples per
  second
• Sample size s bits
• Each second of digitized audio requires rs/8
  bytes
• CD quality r 44100, s 16, hence each second
  requires just over 86 kbytes (k1024), each
  minute roughly 5Mbytes (mono)

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Sound Editing

• Timeline divided into tracks
• Sound on each track displayed as a waveform
• 'Scrub' over part of a track e.g. to find pauses
• Cut and paste, drag and drop
• May combine many tracks from different recordings
  (mix-down)

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Effects and Filters

• Noise gate
• Low pass and high pass filters
• Notch filter
• De-esser
• Click repairer
• Reverb
• Graphic equalizer
• Envelope Shaping
• Pitch alteration and time stretching
• etc

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Compression

• In general, lossy methods required because of
  complex and unpredictable nature of audio data
• CD quality, stereo, 3-minute song requires over
  25 Mbytes
• Data rate exceeds bandwidth of dial-up Internet
  connection
• Difference in the way we perceive sound and image
  means different approach from image compression
  is needed

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Audio Formats

• Platform-specific file formats
• AIFF, WAV, AU
• Multimedia formats used as 'container formats'
  for sound compressed with different codecs
• QuickTime, Windows Media, RealAudio
• MP3 has its own file format, but MP3 data can be
  included as audio tracks in QuickTime movies and
  SWFs

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MIDI

• Musical Instruments Digital Interface
• Instructions about how to produce music, which
  can be interpreted by suitable hardware and/or
  software
• cf. vector graphics as drawing instructions
• Standard protocol for communicating between
  electronic instruments (synthesizers, samplers,
  drum machines)
• Allows instruments to be controlled by hardware
  or software sequencers

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iPOD

• The bundled software used for transferring music
  is called iTunes.
• Software
• iTunes Store
• File storage
• iTouch - First iPod with Wi-Fi and a Multi-Touch
  interface. Features Safari browser and wireless
  access to the iTunes Store and YouTube.

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Feedback survey

• Online on my web site
• Week 11
• Previous years exam papers will also be there

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Tuesday class

• Week 11 revision
• Revision class this is instead of the week 12
  lecture 2nd January 12.00 - until, whenever
  we get bored - 16G42Provisional Date
• Exam Monday 5th January 9.30 in Sports Hall 1
  (5F04, 5F05)
• 3 hours

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Revision class

• NOTE
• As these are revision classes there will be no
  PowerPoint slides made available!
• If you are unable to make the classes ... all the
  information you need is in the previously posted
  slides.