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Multimedia

Multimedia. Continuous Media: Audio, Animation, Video. Sound. Conversion of energy into vibrations in the air. Most sound sources vibrate in complex ways leading to sounds with components at several different frequencies. Frequency spectrum – relative amplitudes of the frequency components.

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Multimedia

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  1. Multimedia Continuous Media: Audio, Animation, Video T.Sharon-A.Frank

  2. Sound • Conversion of energy into vibrations in the air. • 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 20Hz–20KHz, falling off with age.

  3. Use of Audio • Convey Information • Set a mood • Capture attention • Explain a process • Provide personal contact • Tell a story T.Sharon-A.Frank

  4. Nature of Sound • Sound is produced by the vibration of matter. • Pressure variations are created in air surrounding matter. • Pattern of oscillation is called a waveform. T.Sharon-A.Frank

  5. 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.

  6. Basic Sound Concepts • Waveform: • Period • Frequency • Amplitude • Computer Representation of Sound: • Sampling • Quantization T.Sharon-A.Frank

  7. Period • Repeating portion of the sound wave, although sound waves are never perfectly smooth or uniformly periodic. T.Sharon-A.Frank

  8. Frequency • Reciprocal of the period, that is, number of periods in a second; measured in hertz (Hz) or cycles per second. • Human hearing frequency range is from 20Hz to 20KHz: • Infrasound: 0 - 20Hz • Ultrasound: 20KHz - 1GHz • Hypersound: 1GHz - 10THz T.Sharon-A.Frank

  9. Amplitude • Measure of displacement of the air pressure wave from its mean. • Subjectively heard as loudness. amplitude T.Sharon-A.Frank

  10. Sound Wave Example T.Sharon-A.Frank

  11. Idea of Audio Digitization • Smooth continuous curve of waveform is not directly represented in computer. • Amplitude of waveform is measured and recorded at regular time intervals - process is called encoding. • Each interval is called a sample. • Need Analog-to-Digital Converter (ADC). T.Sharon-A.Frank

  12. Audio Digitization • Converting signal from analogue to digital form • Analogue signal can vary continuously; digital isrestricted to discrete values. • Two-stage process: • Sampling – measure the value at discrete intervals. • Quantization – restrict the value to a fixed set of quantization levels.

  13. Digital Sampling Sample Height Samples Time Samples T.Sharon-A.Frank

  14. Digital Quantization Sample Height Example: 3 bit quantization Samples Samples T.Sharon-A.Frank

  15. Audio Encoding (a) A sine wave. (b) Sampling the sine wave. (c) Quantizing the samples to 4 bits. T.Sharon-A.Frank

  16. Process of Sampling Audio T.Sharon-A.Frank

  17. Sampling Rate • Number of samples per second measured in hertz (Hz). • More samples = higher quality = bigger files. • Example: • CD quality = 44,100 Hz (44.1 KHz) • Others: 8,000 Hz, 11,025 Hz, 22,050 Hz T.Sharon-A.Frank

  18. Sampling Size • Number of bits used to represent each sample. • Called also Bit Depth and Sound Resolution. • 8-bit - telephone quality (typical of Web). • 16-bit - CD quality. • Examples: Web quality (11.025 KHz, 8bit) 16 bit, 44.1kHz 8 bit , 44.1KHz T.Sharon-A.Frank

  19. Channels • Audio files can support from 1 to 6 channels of audio information. • Most common: • mono (1 channel) • stereo (2 channels) • 4-6 channels are usually used for surround sound. T.Sharon-A.Frank

  20. Record Settings Menu for Audio T.Sharon-A.Frank

  21. Sample Audio File Formats • aif/aiff • wav • au • mov • MPEG/MP3 (MPEG 1 Level 3) • RA/RAM • MIDI (Musical Instrument Digital Interface) T.Sharon-A.Frank

  22. Audio File Formats (platform specific) • aif (aiff) • Audio Interchange File Format • original audio format for Mac • supported by Windows and other platforms • wav • Waveform Audio File Format • original Windows audio file format • supported on Mac • au • u-law (myoo-law) • Unix standard audio format T.Sharon-A.Frank

  23. Audio File Formats (container formats) • mov (qt) • QuickTime, not just Apple/MAC • mpg (mpe, mpeg) • Moving Pictures Expert Group • High quality, excellent compression file format • Files tend to be small and sound good • ra (ram) • RealAudio T.Sharon-A.Frank

  24. Real Audio Format • First example of streaming audio on the Web. • Quality like that of an AM radio station. • Best used for narration and not for music or other sounds. • Must have RealPlayer on your system to listen to files. T.Sharon-A.Frank

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

  26. MIDI and Computers • MIDI interface allows a computer to send MIDI data to instruments. • Store MIDI sequences in files, exchange them between computers, incorporate them into multimedia. • Computer can synthesize sounds on a sound card, or play back samples from disk in response to MIDI instructions • Computer becomes primitive musical instrument (quality of sound inferior to dedicated instruments).

  27. Uncompressed Audio Digital Telephony • Sampled at 8KHz (8K cycles per second) • Quantized to 8 bits per sample (1 Byte) => 64,000bits/s • Bandwidth = 64,000/1,024 = Total: 62.5Kb/s T.Sharon-A.Frank

  28. Uncompressed Stereo Audio CD Quality • Sampled at 44.1KHz (44.1K cycles per second) • Quantized to 16 bits per sample (2 bytes) • Two channels for stereo • Bandwidth = 2 * 44,100 * 16 = 1,411,200b/s 1,411,200/1024= 1,378Kb/s Total: ~1.4Mb/s T.Sharon-A.Frank

  29. Animation • The creation of moving pictures one frame at a time: • Literally 'to bring to life‘. • e.g. make a sequence of drawings on paper, in which a character's position changes slightly in each drawing. • Photograph drawings in sequence, using movie camera that advances one frame at a time. • Play back resulting film – character will move.

  30. Use of Animation • Capture the viewer’s attention, entertain, or promote. • Explain a system or process. • Set a mood or create an on-screen environment. T.Sharon-A.Frank

  31. Animation Principles • Persistence of vision: • object seen by human eye remains mapped on retina for a brief time after viewing. • display series of images rapidly and they blend together to create illusion of movement. • requires at least 16 frames per second (fps) to look seamless. • Television: displayed at 30 frames per second. • Movies: displayed at 48 frames per second. T.Sharon-A.Frank

  32. Cell Animation (Frame Animation) • Start with first and last image in motion (called keyframes). • Draw images between keyframes (process called tweening/morphing) - small changes between images. • Images are then layered onto background scene. • Images displayed rapidly • 15/24/30 frames per second. T.Sharon-A.Frank

  33. Captured Animation • Logic and procedural concepts are same as in cell animation (keyframe, tweening, layering techniques). • But use computer and video camera. • Frame grabbing – record each frame to disk. • Edit non-linearly like for video. • Can also use scanner or digital still camera, or create each frame in a graphics program (e.g., Painter).

  34. Cell-based Techniques • Morphing: • uses frames to create illusion of one object changing into another • more keyframes = smoother morph. • Need at least 15 frames per second. • Professional quality uses 24-30 frames per second. • Cell-based animation is done more easily on computer than by hand. • Easier to create and process than movies. T.Sharon-A.Frank

  35. Path-based Animation (Vector Animation) • Create animated objects by following object’s transition over a line or vector. • Artist creates one drawing and a path. • Computer program manipulates object by drawing frames as object travels over the path. T.Sharon-A.Frank

  36. Sample Animation File Formats • Animated GIF • mov (QuickTime) • SWF (Flash) • PNG (PortableNetwork Graphics) T.Sharon-A.Frank

  37. Animated GIFs • Sequence of images can be stored in a single GIF file, and displayed one after another by a Web browser or other software: • No browser plug-in required • Can specify looping, delay between frames • 256 colour palette • No sound.

  38. SWF • Popular Web animation format. • Usually generated by Macromedia Flash. • Vector animation format • Motion represented as numerical operations on vector data. • Can also include bitmapped images (e.g., as backgrounds).

  39. Video • Video is sequence of images displayed at constant rate. • Rate is in frames per second (fps). • Needs around 10-15 fps for smooth motion. • For example, video is displayed at 24-30 fps. T.Sharon-A.Frank

  40. Use of Video • Tell a story • Entertain an audience • Explain a complex process • Personalize a Multimedia experience T.Sharon-A.Frank

  41. Movie - Characteristics • Built from Frames - Each frame is an Image • Image characteristics (i.e., resolution, colors) Clip Scene Shot Frame Frame T.Sharon-A.Frank

  42. A movie may consist of several files T.Sharon-A.Frank

  43. Sample Video File Formats • MOV • AVI • RA/RAM • ASF • WMV • MPEG1/2/4 • FLV T.Sharon-A.Frank

  44. MPEG • MPEG = Moving Picture Experts Group. • Family of compression algorithms. • High compression rate. • Algorithm stores only changes from one frame to another rather than each entire frame. • Video info then encoded using DCT. • Lossy compression but loss of data is generally imperceptible to human eye. T.Sharon-A.Frank

  45. MPEG Video Format • ISO/IEC MPEG (Moving Picture Experts Group) Series of standards including: • MPEG-1: used for video CD 352x240 @30 frames/second. • MPEG-2: used for compressing DVD and high-definition television (HDTV). • MPEG-4: used to transmit audio, video, and graphics at low bitrate – can be delivered over very slow connections (56 Kbps). T.Sharon-A.Frank

  46. Video Acquisition • TV set and PC monitor look similar. • TV is analog • Gets info from continuously varying broadcasting waves. • PC is digital • Data displayed is digital. • Digitization performed by video capture card. • Typical card is combination of hardware and software. • Capture card typically creates uncompressed files that then must be passed into a codec chip or software. T.Sharon-A.Frank

  47. Issues Affecting Video File Size • Movie Length - simple principle: shorter video clips result in smaller files. • Frame Size - full-screen video is 640x480. Typical frame size on WWW = 160x120 although can handle 320x240. • Frame Rate: • TV quality = 30 fps • Web = 15 (or even 10) fps. T.Sharon-A.Frank

  48. Video Presentation • TV • PAL • NTSC • SECAM • HDTV • Computer Display T.Sharon-A.Frank

  49. TV Standards • NTSC (National Television Standard Committee) • Used by TV and video industries in US and Japan Taiwan, parts of South America, … • PAL (Phase Alternating Line) • Used in Western Europe, Australia & New Zealand, China , … • SECAM (Sequential Color and Memory) • France and former Soviet Union • Standard only used for transmission • Very different technology than PAL.

  50. Video (PAL, HDTV) Bandwidth • PAL Resolution: 640 x 480 • 3 bytes per pixel • Frame rate: 25 fps • Bandwidth: 640 * 480 * 25 * 24 = 184,320,000b/s Total: ~176Mb/s HDTV bandwidth increased by factor of 5.33:~936Mb/s T.Sharon-A.Frank

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