Introduction to SDI Interface Standards-Knowledge Encyclopedia-Shenzhen Kai Mo Rui Electronic Technology Co. LTD

Introduction to SDI Interface Standards

Source：Shenzhen Kai Mo Rui Electronic Technology Co. LTD2026-07-07

This document delivers an in-depth introduction to the SDI interface standard. It covers a completely different application scope from LVDS yet serves as an indispensable standard for professional video transmission.

I. What Is SDI?

Full Name: Serial Digital Interface

Essence: A point-to-point serial link standard dedicated to transmitting uncompressed digital video, audio and associated auxiliary data.

Core Features: Real-time processing, superior image quality and zero latency. It has become the industry benchmark for broadcast television, professional film production, live events and other verticals.

Standards Body: A suite of specifications formulated and maintained by the Society of Motion Picture and Television Engineers (SMPTE).

II. Core Working Principles & Characteristics

Uncompressed Transmission

Unlike consumer-grade interfaces such as HDMI and DisplayPort that may carry compressed data, SDI transmits raw pixel data (most commonly YCbCr 4:2:2). This preserves maximum image fidelity with zero processing latency, a critical advantage for broadcast-grade workflows requiring real-time switching and signal manipulation.

Coaxial Cable-Based Architecture

SDI was originally engineered around 75-ohm coaxial cables paired with BNC connectors. Coaxial cabling delivers robust shielding and strong anti-interference performance, ideal for long-distance high-quality signal delivery.

Self-Synchronization & Clock Recovery

SDI multiplexes video payloads, audio streams, timing signals (horizontal sync, vertical sync) and auxiliary data into a single serial data stream.

Receiving devices recover clock signals directly from the serial stream for accurate data parsing, eliminating the need for separate clock wiring.

Scrambling & NRZI Encoding

To guarantee stable transmission and DC balance (facilitating cable coupling), raw SDI data undergoes scrambling via a polynomial generator, followed by NRZI (Non-Return-to-Zero Inverted) encoding.

This generates sufficient signal transitions for the receiver’s clock recovery circuit to achieve stable locking, while suppressing low-frequency signal components.

III. Physical Interfaces & Cables

Connector

Virtually all SDI deployments adopt BNC connectors. This bayonet-locking connector delivers secure, stable mating with minimal risk of accidental disconnection.

Cable: 75Ω Coaxial Cable

Cable quality directly determines maximum transmission distance:

SD-SDI: Conventional video cables support transmission over hundreds of meters.
HD/3G/6G/12G-SDI: Require premium low-loss coaxial cables (e.g., Belden 1694A). Maximum reach shortens as bitrate rises:
- HD-SDI: Approximately 100 meters
- 3G-SDI: Approximately 100 meters
- 12G-SDI: 70–100 meters with stringent cable performance requirements

IV. Ancillary Data (ANC Packets)

Beyond video payloads, the SDI data stream reserves extensive ancillary data space to carry:

Embedded audio: Up to 16 channels (or more) of uncompressed digital audio, synchronized with video without separate audio cabling.
Timecode: VITC, LTC and other timecode formats.
Captions and graphic overlay information.
Metadata.

This all-in-one single-cable architecture drastically reduces wiring complexity in professional broadcast systems.

V. Primary Application Scenarios

SDI stands as the dominant transmission medium across all professional video industries, with typical deployments including:

Broadcast studios: Interconnections between cameras, video switchers, video recorders, character generators and monitors.
Outside broadcast (OB) vans.
Post-production suites: Non-linear editing systems, color grading workstations and disk recorders.
Digital cinema (D-Cinema): While DCP relies on file-based delivery, internal equipment links frequently adopt SDI.
High-end medical imaging and premium surveillance systems demanding stable, high-fidelity video streams.

The SDI interface is synonymous with reliability, real-time responsiveness and premium image quality within professional video workflows. Though its coaxial cable foundation represents a mature design, it delivers unmatched stability and long-distance signal transmission capability. Its integrated all-in-one design for video, audio and auxiliary data greatly streamlines professional system integration.

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