Multimedia Systems by Sahil Punni


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This slide on Multimedia Systems is an ongoing effort to put together my lectures and notes compiled over several years of studying the Multimedia Systems at one of the most reputed university in the country. I realized it is a more natural fit for my thinking on the matter of books. I do not care to make money off of a "student". The knowledge contained in these lectures is not my invention, it may have the imprint of my interpretation and to that extent is my creation with all its flaws. Therefore, I see myself as merely a conduit of this knowledge. It is for you the reader to decide what this is worth to you. If this is worth something to you then hopefully you will participate in similar acts of knowledge dissemination as you are able.
Most of the topics are complete with some that I plan to fill with time. For each topic that I already have content there is my audio that goes with the powerpoint slides. The pdfs are simply prints of the powerpoint slides. On some lectures I have notes associated with the powerpoint slides. Also where relevant I used animation in powerpoint when I felt it served as an aid towards comprehension.

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Multimedia Systems by Sahil Punni

  1. 1. DIGITAL AUDIO AND VIDEO Sahil Punni 7/10/2014 1
  2. 2. CONTENTS  Audio  How we hear Sound?  Basic Sound Concepts  Computer Representation of Audio  Audio Encoding  Audio Formats  Video Encoding  Video Formats  Conclusion  Additionals : Digital Audio and Video Editing Softwares Explained 7/10/2014 2
  3. 3. AUDIO  Sound is a continuous wave that travels through the air.  The wave is made up of pressure differences. 7/10/2014 3
  4. 4. HOW DO WE HEAR SOUND? 7/10/20144
  5. 5. BASIC SOUND CONCEPTS  Frequency represents the number of periods in a second (measured in hertz, cycles/second)  Human hearing frequency range: 20 Hz - 20 kHz (audio), voice is about 500 Hz to 2 kHz.  Amplitude of a sound is the measure of displacement of the air pressure wave from its mean. 7/10/20145
  6. 6. COMPUTER REPRESENTATION OF AUDIO • Speech is analog in nature and it is converted to digital form by an analog-to-digital converter (ADC). • A transducer converts pressure to voltage levels. • Convert analog signal into a digital stream by discrete sampling • Discretization both in time and amplitude (quantization) 7/10/2014 6
  7. 7. AUDIO ENCODING (1) Audio Waves Converted to Digital • electrical voltage input • sample voltage levels at intervals to get a vector of values: (0, 0.2, 0.5, 1.1, 1.5, 2.3, 2.5, 3.1, 3.0, 2.4,...) • A computer measures the amplitude of the waveform at regular time intervals to produce a series of numbers (samples). • The ADC process is governed by various factors such as sample rate and quantization: binary number as output 7/10/2014 7
  8. 8. AUDIO ENCODING (2) • Sampling Rate: rate at which a continuous wave is sampled (measured in Hertz) • Examples: CD standard - 44100 Hz, Telephone quality - 8000 Hz • The audio industry uses 5.0125 kHz, 11.025 kHz, 22.05 kHz, and 44.1 kHz as the standard sampling frequencies. These frequencies are supported by most sound cards. 7/10/2014 8
  9. 9. AUDIO ENCODING (3)  The best-known technique for voice digitization is Pulse-Code Modulation (PCM).  Voice 4000 Hz What is the PCM sampling rate?  PCM provides analog samples which must be converted to digital representation. Each of these analog samples must be assigned a binary code. Each sample is approximated by being quantized as explained next. 7/10/2014 9
  10. 10. AUDIO ENCODING (4)  Quantization (sample precision): the resolution of a sample value. Samples are typically stored as raw numbers (linear PCM format) or as logarithms (u-law or A-law) Quantization depends on the number of bits used measuring the height of the waveform Example: 16-bit CD quality quantization results in over 65536 values 7/10/2014 10
  11. 11. AUDIO FORMATS (1) 7/10/2014 11 • Audio Formats are described by the sample rate and quantization • Voice quality: 8-bit quantization, 8000 Hz u-law mono (8kBytes/s) • 22 kHz 8-bit linear mono (22 kBytes/second) and stereo (44 kBytes/s) • CD quality 16-bit quantization, 44100 Hz linear stereo (176.4 kBytes/s = 44100 samples x 16 bits/sample x 2 (two channels)/8000)
  12. 12. AUDIO FORMATS (2)  Available formats on SUN au - Sun File Format wav - Microsoft RIFF/waveform Format al - Raw A-law Data Format u - Raw u-law Data Format snd - NeXT File Format  Available formats on Microsoft-Windows-based systems ( RIFF formats): Waveform audio file format for digital audio hardware MIDI file format for standard MIDI files Audio Video Interleaved (AVI) Indeo file format 7/10/2014 12
  13. 13. AUDIO FORMATS (3) • RIFF (Resource Interchange File Format) forms the basis of a number of file formats. RIFF (similarly to TIFF - Tagged Image File Format) is a tagged file format. Tags allow applications capable of reading RIFF files to read RIFF files by another application, hence the word interchange in RIFF. • Other Formats/Players - RealPlayer 7 (Windows NT) with RealAudio, MP3 (MPEG Audio Layer 3) audio, Midi players; MP3 players ( 7/10/2014 13
  14. 14. VIDEO ENCODING (1) 7/10/2014 14
  15. 15. VIDEO (COLOR) ENCODING (2) • During the scanning, a camera creates three signals: RGB (red, greed and blue) signals. • For compatibility with black-and-white video and because of the fact that the three color signals are highly correlated, a new set of signals of different space are generated. • The color systems correspond to the standards such as NTSC, PAL, SECAM (conventional systems). 7/10/2014 15
  16. 16. VIDEO ENCODING (3) • For transmission of the visual signal we use three signals: 1 luminance (brightness- basic signal) and 2 chrominance (color signals). • In NTSC signal the luminance and chrominance signals are interleaved; • The goal at the receiver is : (1) separate luminance from chrominance components, and (2) avoid interference between them (cross-color, cross luminance) 7/10/2014 16
  17. 17. VIDEO FORMAT (1)  NTSC (National Television Systems Committee) TV Format (USA TV Standard) Analog video format Color carrier 4.429 MHz; refresh rate 30 Hz (29.92Hz); 4.2 MHz for luminance, 1.5 MHz for eac of the two chrominance channels  Resolution: 833x635 picture elements  Refresh Rate: 30 Hz  Aspect Ratio: 4:3  Interlaced format : Each frame is composed of two consecutive fields, each containing half the scanning lines of a picture, which are scanned and presented in interlaced mode. 7/10/2014 17
  18. 18. VIDEO FORMATS (2)  High Definition TV (HDTV) Research on HDTV started in Japan 1968 Current TV standard  Resolution: twice as many horizontal and vertical columns and lines than conventional systems (NTSC) Two resolution systems  High 1440 Level with 1,440x1,152 pixels  High Level with 1,920x1,152 pixels  Frame rate: 50 or 60 frames per second  Aspect Ratio: 16:9  Interlaced and/or progressive scanning formats Conventional systems use interlaced (alternation of scanning lines) format HDTV similar to computer displays, uses progressive scanning 7/10/2014 18
  19. 19. SUMMARY • Audio and Video Encoding principles are very important, set the basis for digitization • Different Digital Audio, Image and Video Formats, not much standardization across continents/countries, hence difficult to build multimedia systems • Multimedia systems are behind other systems such as web systems, grid systems, operating systems, …… due to the large space in audio and video formats. 7/10/2014 19
  20. 20. SPECIAL ADDITIONALS  Adobe Audition  Magix Music Maker  Media Player Classic  PhotoDesk Pro Show  Windows Media Player  VLC Player  AV Karaoke Maker  Converters : flv to mp3 converter 7/10/2014 20
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