Digitizing and Delivering Audio and Video

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Don't hesitate to comment below if you have any questions or additional phrases Digitizing and Delivering Audio and Video Jon DunnJenn Riley IU Digital Library Program Digital Library Brown Bag SeriesFebruary 11, 2005 ,Some questions to ask when starting a project What is the purpose of digitization? Preservation/archiving Delivery to users: network, CD-ROM, DVD Both Who are the users and what is the use? Affects quality requirements Where are the users? Network bandwidth How will they get to the content? Metadata, searching, browsing ,Presentation Outline Digitization and capture Audio Video Delivery What’s going on at IU? Available digital audio/video services Digital library projects involving audio/video ,Presentation Outline Digitization and capture Audio Video Delivery What’s going on at IU? Available digital audio/video services Digital library projects involving audio/video ,Typical Audio/Video Workflow Digitization/ Encoding Transcoding Source Master file Compressed derivative files for delivery Editing/cleaning possible ,Tools for Digitization Computer workstation Audio/video source equipment VCR, tape deck, turntable, etc. Analog-to-digital converter May be internal or external (connected to computer via USB or Firewire) Wide range of quality: consumer, professional Audio/video editing, compression software Audio examples: Sound Forge, Bias Peak Video examples: Adobe Premiere, Apple Final Cut Pro, Apple iMovie ,Audio: Source Formats Analog Discs: LPs, 78s, etc. Tapes: open reel, cassette, 8-track Other: wire recordings, cylinders Digital Discs: CD, DVD-Audio Tapes: DAT, ADAT ,Digital Audio Basics Sampled waveform Pulse code modulation, or PCM PCM characteristics which determine quality Sample rate (hertz) Determines frequency range reproduced Sample rate = 2 * frequency range (Nyquist) Sample size (bits) Larger sample size = less quantization noise Number of channels ,Digital Audio: Sampling audio sampling quantization noise Barlow, Multimedia Systems, p. 77. ,CD Audio Sample rate: 44.1 kHz (44,100 samples/second) Sample size: 16 bits Number of channels: 2 (stereo) Bitrate 44100 samples/second * 16 bits/sample * 2 channels = 1.4112 megabits/second ,Master Audio File Formats Two main formats (actually many more) WAV (Microsoft/IBM) AIFF (Apple) All essentially interchangable Header + sample data No true standard (i.e. ISO standards process) in common use WAV is defacto standard Broadcast WAV gaining use ,Audio Compression Most audio compression schemes for music are lossy, based on ‘psychoacoustic’ techniques Based on understanding of human hearing and audio processing Masking principle Subband coding ,Audio Compression:Masking Effect Barlow, Multimedia Systems, p. 73. ,Audio Compression: Standards MPEG-1 Layers 1, 2, and 3 (‘MP3’) Typically 128-384 kilobits/second (for stereo) MPEG-2 Layers 1, 2, and 3 and AAC (Advanced Audio Coding) Typically 96-384 kilobits/second (for stereo) MPEG-4 Improved AAC Synthetic audio Low bit rate parametric audio ,Audio Compression: Proprietary Formats (Codecs) QDesign Music Used with Apple QuickTime RealAudio Used with RealPlayer Windows Media Audio Used with Windows Media Codec: compressor/decompressor ,Video: Source Formats Analog Tape: VHS, Betamax, 8mm, Hi8, Umatic, Betacam SP Disc: Laserdisc, SelectaVision :-) Digital Tape: MiniDV, Digital8, DVCAM, Digital Betacam Disc: Video CD, DVD ,Video is just like a series of still images, right? No. Scanned images Represented as grid of Red-Green-Blue values Master images are uncompressed, lossy compression used for derivatives See Jenn’s Fall 2003 Digitization of Photographs brown bag presentation for more info ,Video is somewhat like a series of still images Video uses Red-Green-Blue color space Pixel resolution (width x height), number of bits per pixel, and frame rate are factors in quality But there’s much more to it… ,Digital Video Basics A video signal consists of luminance and chrominance information Luminance – brightness, varying from
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