Red5 Documentation

Audio and Video Codecs Glossary


AAC (Advanced Audio Coding) – An audio coding standard for lossy digital audio compression. Designed to be the successor of the MP3 format, AAC generally achieves better sound quality than MP3 at the same bit rate.

Opus – A lossy audio codec designed to efficiently code speech and general audio in a single format, while remaining low-latency enough for real-time interactive communication and low-complexity enough for low-end embedded processors.

Speex – A free software speech codec that may be used on VoIP (Voice Over Internet Protocol) applications. Specifically, it is a lossy audio compression format specifically tuned for the reproduction of human speech.


H.264/MPEG-4 AVC (Advanced Video Coding) – A block oriented motion compensation-based video compression codec. It is a standard capable of providing good video quality at substantially lower bit rates than previous standards. It can be implemented in a wide variety of networks and systems and is usable with many protocols.

VP8 – A block-based transform coding format. Very similar to H.264.

  • VP9 – VP9 is the successor to VP8 and competes mainly with MPEG’s High-Efficiency Video Coding (HEVC/H.265).

Codecs used with Red5 by Platform


  • Audio: Opus
  • Video: H264 and VP8


  • Audio: Speex
  • Video: H264


  • Audio: AAC
  • Video: H264