SDI Embedded Audio

showstack / protocols / sdi-embedded-audio

SDI Embedded Audio

Also called Embedded audio, SDI audio.

AES3-derived digital audio mapped into the ancillary data space of an SDI video signal. It carries programme, mix-minus and isolated feeds with the picture instead of on separate audio cables.

Audio transportOpenSMPTEVerified

Stewarded by SMPTE (Society of Motion Picture and Television Engineers).

Maintained by@iibaranov-IGupdated 2026-09-11

Media Large, continuous, on time and in order

Continuous streams that are large enough to be sized properly, and that must arrive in order and on time.

What kills it. Anything that starves the link — usually a management transfer nobody scheduled — and jitter that outruns the receive buffer.

The four flows, and why the model is worth having →

What it carries

Sample rates: 32 kHz, 44.1 kHz, 48 kHz, 96 kHz
Audio bit depth: 24-bit
Audio channels: up to 16
Audio encoding: AES3-derived linear PCM or SMPTE ST 337 non-PCM data

Audio: ST 299-1 carries four groups of four channels at up to 48 kHz. At 96 kHz, each group carries two channels, reducing the maximum to eight.

What goes wrong

Channels travel in groups of four. An embedder or de-embedder configured for the wrong group can pass clean video while returning silence on the expected audio pair.

The 16-channel maximum applies at 32, 44.1 or 48 kHz. At 96 kHz ST 299-1 carries eight channels, so raising the sample rate halves the available channel count.

Audio data and audio control packets occupy different ancillary spaces. Equipment that processes or strips ancillary data can preserve the picture while losing embedded audio or its control information.

Typical use

Camera and replay audio carried with video into a production switcher
Programme and mix-minus feeds through SDI routers and distribution amplifiers
Audio extraction at recorders, monitors and streaming encoders

Sources

SMPTE ST 299-1:2009 — 24-Bit Digital Audio Format for SMPTE 292 — SMPTE primary
SMPTE 299-0:2010 — Roadmap for the 299 Document Suite — SMPTE primary

Understand the mechanism

Show networks Numbers that stand for signals

Something wrong, or missing?

Known gaps on this entry: default_ports, first_published, implementations. If you can source one of them, that is a ten minute pull request.

Edit this entry on GitHub — one file, editable in your browser, and your handle goes on it permanently.

Work at SMPTE (Society of Motion Picture and Television Engineers)? Confirm or correct this entry — it is free, it stays free, and nothing about it is for sale.