WebRTC Audio Codec Opus & Processing Requirements

April 2014

Tsahi

Levent-Levi

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

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) ?

General Codec Characteristics

4/4/2014 4

Complexity CPU Latency

ms

Resiliency Packet loss

IPR Royalty payments

Voice Codec “Features”

4/4/2014 5

Bitrate kbps

Sampling rate kHz

Channels Mono, Stereo, …

Hz and Hearing Ranges

4/4/2014 6

cochlea.org

Narrow, Wide, Super & Full

4/4/2014 7

Opus vs. The World

• Requires a lot of processing power

• Optimized for mobile in Opus 1.1

4/4/2014 8

Opus is Different

1. SILK - low bitrate speech

2. CELT - music and high fidelity

4/4/2014 9

Hybrid what?

4/4/2014 10

SILK CELT

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

Mobile

Getting better on mobile, where the focus is

4/4/2014 12

Servers

No improvements on servers

4/4/2014 13

Where does that leave us?

Architectural decisions of where to position Opus in our network

4/4/2014 14

Thank You!

Tsahi Levent-Levi

http://bloggeek.me

tsahil@bloggeek.me

4/4/2014 15