Audio redundancy (RED) support in CDN

Since build 5.3.414, audio redundancy (RED, RFC2198) is supported while passing media data via WebRTC between CDN nodes. This feature is disabled by default, and may be enabled with the following parameters

codecs=red,opus,alaw,ulaw,g729,speex16,g722,mpeg4-generic,telephone-event,h264,vp8,flv,mpv,h265
cdn_pull_red_audio=true

The settings should be applied on all the CDN nodes.

However, CDN audio profile setup has a priority above cdn_pull_red_audio parameter. If RED is enabled in CDN audio profile on the Edge server

profiles:
 -480p:
  audio:
    codec: red
    rate: 48000
    channels: 2
  video:
    height : 480
    bitrate : 1100
    gop : 50
    codec : h264
...

then Edge server requires RED audio encoding from a Transcoder server even if cdn_pull_red_audio=false on both servers.