Codecs – Everything You Always Wanted to Know

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…