webrtc之入门

webrtc developers

The WebRTC APIs

Three main tasks

• Acquiring audio and video
• Communicating audio and video
• Communicating arbitrary data

Three main JavaScript APIs

• MediaStream(aka getUserMedia)
• RTCPeerConnection
• RTCDataChannel

MediaStream

(Acquiring audio and video)

MediaStream

• Pepresent a stream of audio and/or video
• Can contain multiple ‘tracks’
• Obtain a MediaStream with navigator.getUserMedia()

Constraints

• Controls the contents of the MediaStream
• Media type, resolution, frame rate

  RTCPeerConnection

  (Audio and video communication between peers)

  RTCPeerConnection does a lot

• Signal processing
• Codec handling
• Peer to peer communication
• Security
• Bandwidth management

  WebRTC architecture

  

RTCDataChannel

(Bidirectional communication of arbitrary data between peers)

RTCDataChannel

• Same API as WebSockets
• Ultra-low latency
• Unreliable or reliable
• Secure

Servers and Protocols

(Peer to peer — but we need servers :)

Abstract Signaling

• Need to exchange ‘session description’ objects:
  • What formats I support, what I want to send
  • Network information for peer-to-peer setup
• Can use any messaging mechanism
• Can use any messaging protocol

STUN and TRUN

(P2P in the age of firewalls and NATs)

An ideal world

The real world

STUN

• Tell me what my public IP address is
• Simple server, cheap to run
• Data flows peer-to-peer

TURN

• Provide a cloud fallback if peer-to-peer communication fails
• Data is sent through server, uses server bandwidth
• Ensures the call works in almost all environments

ICE

• ICE: a framework for connecting peers
• Tries to find the best path for each call
• Vast majority of calls can use STUN (webrtcstats.com):

Deploying STUN/TURN

• stun.l.google.com:19302
• WebRTC stunserver, turnserver
• rfc5766-turn-server
• restund

Security

Security throughout WebRTC

• Mandatory encryption for media and data
• Secure UI, explicit opt-in
• Sandboxed, no plugins
• WebRTC Security Architecture

Architectures

Peer to Peer : one-to-one call

clientA <——–> clientB

Mesh: small N-way call

clientA <-------------> clientB
  /|\  \               /   /|\
   |       \    /           |
   |      /       \         |
  \|/   /                  \|/
clientC <--------------> clientD

Star: medium N-way call

clientA <---------> clientB
clientA <---------> clientC
clientA <---------> clientD

MCU: large N-way call

MCU <-------------->clientA
MCU <-------------->clientB
MCU <-------------->clientC
MCU <-------------->clientD
MCU <-------------->clientE
MCU <-------------->clientF
MCU <-------------->clientG