What is an SDI Interface and What Are the SDI Standards?

Serial Digital Interface (SDI) is a digital video transmission standard commonly used in professional broadcasting and video production environments.

Developed by the Society of Motion Picture and Television Engineers (SMPTE), SDI provides a way to transmit uncompressed, high-quality video signals over coaxial cables or fiber optics. Its primary purpose is to ensure that video, audio, and metadata can be transmitted without quality loss over long distances, making it a staple in live event production, studio work, and broadcast setups.

Key Features of SDI

1. Uncompressed Transmission: SDI transmits video in an uncompressed format, maintaining the original quality of the signal without compression artifacts. This is essential for professional-grade video production, where image quality is paramount.

2. Single-Cable Solution: SDI supports both video and audio over a single coaxial cable. This streamlines setups by reducing the number of cables needed for transmission, simplifying integration in complex environments.

3. Long Distance Transmission: SDI signals can travel over long distances—typically up to 100 meters using high-quality coaxial cable—without significant loss of signal integrity. Optical fiber extensions can increase this range even further.

4. High Data Rates: SDI standards support a variety of data rates depending on the video resolution and frame rate. The most common data rates are 270 Mbps (SD-SDI), 1.5 Gbps (HD-SDI), 3 Gbps (3G-SDI), and 12 Gbps (12G-SDI), supporting up to 8K video.

5. Embedded Audio: SDI allows embedding of up to 16 channels of digital audio within the video signal. This feature reduces the need for separate audio cabling and simplifies synchronization.

6. Synchronization and Metadata: SDI supports timecode and other metadata, which helps synchronize multiple camera feeds or maintain consistent video quality across complex systems.

SDI Standards

1. SD-SDI (SMPTE 259M): Introduced for standard definition video, SD-SDI transmits data at 270 Mbps and supports resolutions of 480i/576i.

2. HD-SDI (SMPTE 292M): Developed for high-definition video, HD-SDI operates at 1.5 Gbps, supporting 720p and 1080i resolutions.

3. 3G-SDI (SMPTE 424M): This standard doubles the data rate to 3 Gbps, enabling full 1080p at higher frame rates (60 fps) or stereoscopic 3D video transmission. The 3G-SDI standard is found in PTZOptics Move SE cameras, for example.

4. 6G-SDI: Used for 4K video at 30 fps, 6G-SDI supports resolutions up to 4096x2160.

5. 12G-SDI (SMPTE ST 2082): This standard allows for the transmission of 4K video at 60 fps and supports up to 8K video over a single cable, with a data rate of 12 Gbps. The 12G-SDI standard is found in Lumens VC-A71P cameras, for example.

6. 24G-SDI: Currently emerging, this standard is designed for future 8K video transmission at high frame rates, doubling the data throughput of 12G-SDI.

SDI interfaces are essential for high-quality, uncompressed video transmission in professional settings. With multiple standards ranging from SD to 8K video, SDI provides a versatile, reliable solution for video, audio, and metadata transmission across a variety of applications.