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Codecs – Everything You Always Wanted to Know

Dive into the world of Codecs – from background and concepts to comparisons and features. Learn about voice Codec specifics and its applications in an Avaya environment. Explore the differences between analog and digital encoding, and understand how various Codecs impact file sizes and quality. Discover the importance of Codec selection based on audio type, bandwidth, and CPU usage.

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Codecs – Everything You Always Wanted to Know

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  1. Codecs – Everything You Always Wanted to Know RMAUG Professional Development Series 2/11/09 Dwight Reifsnyder

  2. “If you have an apple and I have an apple and we exchange apples then you and I will still each have one apple. But if you have an idea and I have an idea and we exchange these ideas, then each of us will have two ideas.” George Bernard Shaw

  3. Boulder Valley School District

  4. Codecs – EYAWTK Overview • Codec background and concepts • Comparisons and basic features • Voice Codec specifics • Application in an Avaya environment

  5. What is a Codec? • Codec is short for Coder/Decoder • Just like a Dick Tracy! • But what are the concepts involved?

  6. “Coding” is Changing Form • Examples of coding include: • Pictures • Writing • Music • Language translation • Encryption

  7. Audio Encoding • 1876 Alexander Graham Bell • Audio to electricity • 1894 Guglielmo Marconi • Audio to radio • 1916 Theodore Case • Audio to optical

  8. Analog (Wikipedia) • An analog or analogue signalis any continuous signal for which the time varying feature (variable) of the signal is a representation of some other time varying quantity, i.e. analogous to another time varying signal. Analog is usually thought of in an electrical context; however, mechanical, pneumatic, hydraulic, and other systems may also convey analog signals

  9. Digital Encoding • 1937 - Alec H. Reeves • Pulse Code Modulation invented (PCM) • 1942 - John V. Atanasoff, Clifford Berry • First computer • 1962 – Bell Labs • PCM first used in commercial telephony

  10. Digital (Wikipedia) • A digital system uses discrete (discontinuous) values, usually but not always symbolized numerically (hence called "digital") to represent information. By contrast, non-digital (or analog) systems use a continuous range of values to represent information.

  11. Digital (Wikipedia, continued) • The word digital is most commonly used in computing and electronics, especially where real-world information is converted to binary numeric form as in digital audio and digital photography.

  12. Analog vs. Digital • Analog • Continuous, modulates in direct relation to original data • Digital • Discrete data (individual values) with no intuitive or obvious correlation to original data

  13. Concept Review • Encoding is changing form. Data may be encoded, transmitted, stored, and decoded • Analog (encoding or transmission) • Digital (encoding or transmission)

  14. Digital Encoding - Pictures TIF (TIFF) Tagged Image File Format PNG Portable Network Graphic JPG (JPEG) Joint Photographic Experts Group GIF Graphics Interchange Format

  15. Digital Encoding – File Size TIF (TIFF) 576K No Compression (lossless) PNG 232K No Compression (lossless) GIF 97K Compressed (lossy) JPG (JPEG) 105K Compressed (lossy)

  16. Multiple Codecs • If the pictures all look the same, why do we need different Codecs? • Different types of Codecs are optimized for different types of data

  17. JPG vs. GIF • GIF uses Run Length Encoding (RLE) AAAABBBBBCCCCDDDDDDEEEEEEEE 4A4B4C6D8E • Max of 256 colors, fewer colors=smaller file

  18. JPG vs. GIF • JPG uses multiple steps We should create 8x8 DCT matrix using this formula: DCT = 1/sqr(N), if i=0 ij DCT = sqr(2/N)*cos[(2j+1)*i*3.14/2N], if i > 0 ij N = 8, 0 < i < 7 , 0 < j < 7 in result we have: DCT = |.353553 .353553 . 353553 .353553 . 353553 .353553 .353553 .353553| |.490393 .415818 .277992 .097887 -.097106 -.277329 -.415375 -.490246| |.461978 .191618 -.190882 -.461673 -.462282 -.192353 .190145 .461366| |.414818 -.097106 -.490246 -.278653 .276667 .490710 .099448 -.414486| |.353694 -.353131 -.354256 .352567 .354819 -.352001 -.355378 .351435| |.277992 -.490246 .096324 .416700 -.414486 -.100228 .491013 -.274673| |.191618 -.462282 .461366 -.189409 -.193822 .463187 -.460440 .187195|

  19. JPG Quality vs. File Size JPG (JPEG) Quality “30” – 16K JPG (JPEG) Quality “100” 105k

  20. GIF Quality vs. File Size GIF 32 Colors (lossy) 17K GIF 256 Colors (lossless) 97k

  21. Image (and Audio) Codecs Review • There are many codec choices – the goal is for it to be transparent to the user • Codecs can contain multiple encoding/compression steps • Codec choice should consider type of audio, available bandwidth, and CPU usage

  22. Voice Codecs • There a many audio codecs • Quicktime • Real Player • MP3 • Voice Specific Codecs • Industry Standard (ITU) • Optimized for speech

  23. Common Voice Codecs

  24. Bandwidth, Bandwidth, Bandwidth • For most users, the main consideration in choosing a codec is bandwidth • This can be complex when considering calls between multiple regions

  25. Avaya Bandwidth Calculator http://marketingtools.avaya.com/knowledgebase/ipoffice/general/bandwidth/

  26. Common Voice Codecs

  27. VoIP Delay • Initiator • Encoding (DSP usage) • Transmit • Network transmit • Jitter Buffer • Receiver • Encoding (DSP usage)

  28. VoIP Delay – Graphical Version

  29. Common Voice Codecs

  30. Silence – Not Golden • VAD • Voice Activity Detection • “Clipping” • CNG • Comfort Noise Generation • PLC • Packet Loss Concealment

  31. Avaya Codec Sets

  32. G.722 – Wideband Audio • Human Hearing • 5hz to 20khz • Narrowband Codecs • 200hz to 4khz • Wideband Codecs • 50hz to 7khz

  33. What’s NOT a Codec?

  34. Faxes and Modems • VoIP is not a conducive tofax or modem usage • Special settings • G.711 only • Turns off VAD, CNG, PLC • Relay • Redundancy

  35. Thanks for staying awake… • Two codecs walk into a bar…

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