This document discusses digital audio and video encoding principles. It explains how audio is converted from analog to digital form through sampling and quantization, and how various audio formats like WAV, MP3, and others represent digital audio. It also discusses how video works, including concepts like frame rate, resolution, aspect ratio, and differences between standards like NTSC, PAL, and HDTV. Overall it provides an overview of important concepts for understanding how audio and video are digitized and formatted on computers.

1. DIGITAL AUDIO AND VIDEO
Sahil Punni
7/10/2014
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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
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3. AUDIO
 Sound is a continuous wave that travels through the
air.
 The wave is made up of pressure differences.
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4. HOW DO WE HEAR SOUND?
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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.
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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)
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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
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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.
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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.
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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
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11. AUDIO FORMATS (1)
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• 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. 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
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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 (MP3.com)
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14. VIDEO ENCODING (1)
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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).
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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)
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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.
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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
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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.
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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
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