What are codecs?

A codec is a device or software that encodes or decodes a digital stream or signal for transmission over a data network. Codecs are used for both audio and video. The key difference is that audio codecs compress and decompress sound, while with video, do the same for visual content.

Each can be either:

  • Lossless – compresses files without any loss in quality
  • Lossy – removes some data to reduce file size, often used when bandwidth is limited (e.g., video appearing pixelated)

Why Codecs Matter

Audio and video quality depends on how they're managed:

  • Bit rate
  • Compression
  • Latency
  • Error resilience
  • Output quality

Audio codecs:

Codecs Audio Diagram

  • GSM – 13 Kbps (full rate), 20ms frame size.

  • iLBC – 15Kbps,20ms frame size: 13.3 Kbps, 30ms frame size.

  • ITU G.711 – 64 Kbps, sample-based. Also known as A-law/μ-law.

  • ITU G719 – 32/48/64/128 Kbps, 28 ms Frame Size.

  • ITU G.722 – 48/56/64 Kbps.

  • ITU G.723.1 – 5.3/6.3 Kbps, 30ms frame size.

  • ITU G.726 – 16/24/32/40 Kbps.

  • ITU G.728 – 16 Kbps.

  • ITU G.729 – 8 Kbps, 10ms frame size.

  • Speex – 2.15 to 44.2 Kbps.

  • LPC10 – 2.5 Kbps.

  • DoD CELP – 4.8 Kbps.

Video codecs:

Codecs Video Diagram

  • VP8 is the codec used for the encoding and decoding of high definition video as either a file or a bit-stream for viewing. The VP8 codec is – in contrast to the H.264 codec – free for use.

  • H.264/MPEG-4 Part 10 or AVC (Advanced Video Coding) is currently one of the most commonly used video formats for the recording, compression and video playback in high definition. In contrast to VP8, H.264 is not free.

Further reading

Last Updated
This document was last updated on 4 July 2025
https://www.3cx.com/pbx/codecs/