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 1894 Guglielmo Marconi
Audio to electricity
1894 Guglielmo Marconi
Audio to radio
1916 Theodore Case
Audio to optical

8. Analog (Wikipedia)
An analog or analogue signal is 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)
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 Digital
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. AAAABBBBBCCCCDDDDDDEEEEEEEE
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 =
| |
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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 Voice Specific Codecs Quicktime
Real Player
MP3
Voice Specific Codecs
Industry Standard (ITU)
Optimized for speech

23. Common Voice Codecs ITU-T Codec Standard Coding Scheme Used Bit Rate
Encoding Delay Time
Mean Opinion Score
G.711
PCM
64 kbps
<1 msec
4.7
G.722
SB-ADPCM
4 msec
4.5 
G.726
ADPCM
32 kbps
1 msec
4.2
G.728
LC-CELP
16 kbps
2 msec
G.729
CS-ACELP
8 kbps
15 msec
G.723.1
MPMLQ
6.3 kbps
37.5 msec
3.98
ACELP
5.3 kbps
3.5

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

26. Common Voice Codecs ITU-T Codec Standard Coding Scheme Used Bit Rate
Encoding Delay Time
Mean Opinion Score
G.711
PCM
64 kbps
<1 msec
4.7
G.722
SB-ADPCM
4 msec
4.5 
G.726
ADPCM
32 kbps
1 msec
4.2
G.728
LC-CELP
16 kbps
2 msec
G.729
CS-ACELP
8 kbps
15 msec
G.723.1
MPMLQ
6.3 kbps
37.5 msec
3.98
ACELP
5.3 kbps
3.5

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

28. VoIP Delay – Graphical Version

29. Common Voice Codecs ITU-T Codec Standard Coding Scheme Used Bit Rate
Encoding Delay Time
Mean Opinion Score
G.711
PCM
64 kbps
<1 msec
4.7
G.722
SB-ADPCM
4 msec
4.5 
G.726
ADPCM
32 kbps
1 msec
4.2
G.728
LC-CELP
16 kbps
2 msec
G.729
CS-ACELP
8 kbps
15 msec
G.723.1
MPMLQ
6.3 kbps
37.5 msec
3.98
ACELP
5.3 kbps
3.5

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

31. Avaya Codec Sets G.711A (a-law) G.711MU (m-law) G.722-64k G.722.1-24k
G.726A-32k
G.729
G.729B
G.729AB
SIREN14-24k
SIREN14-32k
SIREN14-48k
SIREN14-S48k
SIREN14-S56k
SIREN14-S64k
SIREN14-S96k

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

33. What’s NOT a Codec? G.xxx e.g. G.722, G.711 Voice Encoding H.xxx
e.g. H.323, H.264
Call Control
V.xxx
e.g. V.32, V.90
Modem Encoding
T.xxx
e.g. T.30, T.38
Fax Control

34. Faxes and Modems VoIP is not a conducive to fax 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…