WebRTC's mandatory codecs are G.711 and Opus. What exactly Opus is, how does it stacks up versus other audio codecs and what challenges does it pose for developers?

1. WebRTCAudio Codec
Opus & Processing Requirements
April 2014
Tsahi
Levent-Levi

2. Codec Types
• Throw away things that are not perceived by the human ear and
eye
• Compress the hell out of the rest
• RTC = Low latency in encoding and decoding
4/4/2014 2

3. Media Codecs for WebRTC
No Mandatory To Implement (MTI) video codec yet
(but we don’t care about it in this session)
4/4/2014 3
Codec Use Status
G.711 Narrow band, selected for PSTN and VoIP
interworking
MTI
Opus New flexible audio codec. Narrow to wideband
support; Support for Speech & Music
MTI
VP8 Google’s open source codec ?
H.264 Video codec (MPEG-LA licensing) ?

4. General Codec Characteristics
4/4/2014 4
Complexity
CPU
Latency
ms
Resiliency
Packet loss
IPR
Royalty payments

5. Voice Codec “Features”
4/4/2014 5
Bitrate
kbps
Sampling rate
kHz
Channels
Mono, Stereo, …

6. Hz and Hearing Ranges
4/4/2014 6
cochlea.org

7. Narrow, Wide, Super & Full
4/4/2014 7

8. Opus vs. The World
• Requires a lot of processing power
• Optimized for mobile in Opus 1.1
4/4/2014 8

9. Opus is Different
1. SILK - low bitrate speech
2. CELT - music and high fidelity
4/4/2014 9

10. Hybrid what?
4/4/2014 10
SILK CELT

11. Guidelines
• SILK modified to fit CELT
• FEC inherent in SILK
• All flow control done in-band
• Support hybrid modes of operation
4/4/2014 11

12. Mobile
Getting better on mobile, where the focus is
4/4/2014 12

13. Servers
No improvements on servers
4/4/2014 13

14. Where does that leave us?
Architectural decisions of where
to position Opus in our network
4/4/2014 14

15. Thank You!
Tsahi Levent-Levi
http://bloggeek.me
tsahil@bloggeek.me
4/4/2014 15