Professional 12 Gigabit Serial Digital Interface for single-link 4K uncompressed video transmission over 100m distances with embedded audio, timecode, and zero latency.
Definition
12G-SDI (12 Gigabit Serial Digital Interface) is a video transmission standard for data rates up to 12 Gigabits per second over a coaxial cable. The interface transmits 4K UHD video signals at 60 frames per second.
12G-SDI supports uncompressed 4K signals (3840×2160) and Cinema 4K formats (4096×2160) with 4:2:2 and 4:4:4 color sampling. The standard is backward compatible with 6G-SDI, 3G-SDI, and HD-SDI.
Technical Specifications
Bandwidth & Data Rate:
- Data Rate: 12.5 Gigabits per second (11.88 Gigasymbols/s with 8B/10B encoding)
- Symbol Rate: 11.88 Gsymbol/s
- Effective Video Bandwidth: approx. 10.692 Gbps after encoding
- Encoding: 8B/10B run-length-limited code
Supported Formats:
- 4K (3840×2160) @ 60fps (4:2:2 or 4:4:4)
- Cinema 4K (4096×2160) @ 60fps (4:2:2 or 4:4:4)
- UHD (3840×2160) @ 50fps and 59.94fps
- DCI 4K @ 24fps and 25fps
- Full HD/HD Formats (backward compatible)
Audio & Metadata:
- Embedded Audio: up to 64 audio channels (16 groups of 4 channels)
- Timecode: LTC and VITC transmission
- Metadata: ANC (Ancillary Data) for timecode, closed captions, picture source information
Connector Types & Cables:
- Connectors: 75 Ohm BNC connectors (for coaxial) or ST Fiber connectors (for fiber optic)
- Coaxial Cable: 12G-SDI certified RG-11 or RG-12 coaxial cable
- Maximum Coaxial Cable Length: 100 meters (with RG-11 high-grade)
- Maximum Fiber Optic Cable Length: up to 10 kilometers (multimode) or 40km (singlemode)
Impedance & Signal Quality:
- Characteristic Impedance: 75 Ohm
- Level Ratio: 1 V (sync tip to peak white)
- Jitter Tolerance: <0.2 UI (Unit Interval) at real-time delay
Practical Application
Main Areas of Use:
- Live Events & Broadcasting: Multi-camera productions with live switching, studio broadcasts, remote productions. Low latency enables live monitoring and real-time decisions without noticeable delay.
- UHD/4K Film Production: External recorders like Blackmagic Video Assist Pro or Atomos Ninja V+ use 12G-SDI for lossless 4K recording. The Director of Photography and camera operator see accurate color and exposure on external monitors for informed creative decisions.
- Multi-Camera Setups: Multiple cameras with 12G-SDI output feed a video mixer (e.g., ATEM series) with direct 4K forwarding or scaling. Enables complex production workflows without data bottlenecks.
- Post-Production & Color Grading: Real-time monitoring during editing and grading. Color-calibrated reference monitors with 12G-SDI input display exact image quality without losses from HDMI conversion.
- Overhead Cameras & Specialized Rigs: Cameras on drones, jibs, or cranes transmit 4K signals over 100m cable lengths to control stations without repeaters.
Practical Advantages over HDMI:
- Robustness: Less susceptible to interference in large productions with many wireless systems
- Distance: 100 meters with one cable vs. HDMI max. 30 meters
- Professional Standard: Long-term availability, support from the broadcast industry
- Latency: <1ms transmission delay compared to HDMI ~50-100ms
Device Ecosystem
Cameras with 12G-SDI:
- Sony FX30 / FX3 / Venice Cineline (with optional SDI output module)
- Blackmagic Ursa Broadcast / Ursa Mini Pro 12G
- Panasonic Lumix BS1H (with adapter interface)
- RED Cameras (with optional I/O module)
- Canon EOS R5C (via USB-C to converter box)
Monitors & Video Reference:
- Atomos Ninja V+ (12G-SDI Recorder/Monitor)
- Blackmagic Video Assist Pro 7" (12G-SDI Input/Output)
- SmallHD 702 Touch (12G-SDI Monitor, being discontinued)
- ATEN ProScale (Mixer with scaler functions)
Mixers & Switchers:
- Blackmagic ATEM Pro ISO (6x 12G-SDI Input)
- Grass Valley Ignite (Broadcast suite for video routing)
- Yamaha CL5/QL5 (with optional SDI expansion board)
Converters & Routers:
- Blackmagic Mini Converter (SDI to HDMI / Optical Fiber)
- AJA Converter Line (12G-SDI to various formats)
- Ross OverDrive (Multi-format router / scaler)
Workflow Integration
Typical 4K Live Workflow:
- Sony FX30 → 12G-SDI (via USB-C adapter) → Blackmagic Video Assist
- Video Assist displays live monitoring on 7" screen with waveform/histogram
- Video Assist records ProRes RAW or ProRes onto SSD
- HDMI loop to Director's Monitor for the director
- Timecode sync via embedded LTC
Post-Production Workflow:
- Video Mix (ATEM with 4 cameras) → DeckLink Capture Card
- Real-time editing in DaVinci Resolve with 12G-SDI monitoring
- Calibrated reference monitor (Flanders Scientific) displays exact image
- Export and final archiving
Backward Compatibility
12G-SDI is fully backward compatible:
- 12G-SDI input accepts 6G-SDI signals (with automatic detection)
- 6G/3G/HD-SDI devices do not recognize 12G-SDI but accept converted signals
- Simple passive cable adapters
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