SDI Output

SDI (Serial Digital Interface) is a professional video transport standard used widely in broadcast, live event, and AV installation environments. In WATCHOUT, SDI is one of the five output devices alongside GPU, ST 2110, NDI®, and Virtual. Choosing SDI routes the rendered display output through a dedicated SDI capture/output card installed in the Runner node, delivering an uncompressed digital video signal over coaxial BNC cabling.

SDI is the right choice when your downstream equipment — video switchers, LED processors, recording systems, or broadcast infrastructure — expects a baseband SDI signal rather than a direct GPU output or network-based stream.

Configuring an SDI Display

To set up a display for SDI output:

1. Select the display in the Stage or Device list.
2. In Device Properties → Output, set the Output Type to SDI.
3. Assign the Channel number corresponding to the physical SDI output connector on the installed card.
4. Set the Resolution to match the expected downstream signal format.
5. Choose the appropriate SDI Link Type for the target resolution and bandwidth.

SDI Link Types

The link type determines how many physical SDI connections are used to transport a single display's output. Higher resolutions and frame rates require more bandwidth than a single SDI link can carry, so multiple links are bonded together:

• Single-Link — uses one SDI connection. Supports resolutions up to HD (1920×1080) at standard frame rates on 3G-SDI, or SD formats on HD-SDI. This is the default and most common configuration.
• Dual-Link — uses two SDI connections bonded together, doubling the available bandwidth. Required for resolutions or color depths that exceed single-link capacity, such as 1080p at higher frame rates or some 2K formats with extended bit depth.
• Quad-Link Interleaved — uses four SDI connections with the image samples interleaved across the links. This supports UHD/4K resolutions (3840×2160) by distributing alternating pixel data across all four cables.
• Quad-Link Quadrant — uses four SDI connections where each link carries one spatial quadrant of the full image. This is an alternative 4K transport method where each cable transmits a distinct quarter of the frame. Some downstream equipment prefers one quad-link method over the other, so check your receiver's specifications.

Channel Assignment

The Channel property is an index into the Deltacast VideoMaster SDK's output list on the Runner node, starting at 1. SDI and ST 2110 share the same VideoMaster channel namespace — channels are enumerated across all Deltacast boards on the node, not per board. With an 8-port SDI board and a 4-channel ST 2110 board in the same node, the SDI board might occupy channels 1–8 and the ST 2110 board channels 9–12. The exact ordering follows each card's PCIe address and depends on which PCIe slot the board is connected to.

When using dual-link or quad-link modes, the channel number refers to the first connector in the group — the card automatically bonds the required number of adjacent outputs.

Color and Signal Settings

SDI output in WATCHOUT uses the following signal characteristics:

• Color Depth — 8 or 10 bits per component. SDI shares the Deltacast output pipeline with ST 2110, so the choices match.
• Color Space — Rec. 601, Rec. 709, Rec. 2020, Rec. 2100 HLG, or Rec. 2100 PQ. Default is Rec. 709, which matches the standard encoding expected by most professional SDI equipment.
• Interlaced — enable this toggle when the downstream equipment requires an interlaced signal (e.g., 1080i for broadcast contribution). When disabled, the output is progressive.

Max Quality Mode

The Render with maximum quality toggle uses 16-bit color for compositing. It only has an effect on 8-bit displays — higher bit-depth outputs already use higher precision for compositing. Disable it on integrated GPUs to reduce pixel bandwidth when the extra precision is not needed.

Genlock

In multi-display SDI environments, frame-accurate synchronization is critical to prevent tearing or timing mismatches between outputs. WATCHOUT supports Genlock SDI, which locks the frame output timing of SDI displays to an external reference signal (typically blackburst or tri-level sync) fed into the black burst connector on the Deltacast SDI board.

Genlock is controlled as a show-level property (not per-display). When enabled, all SDI outputs across the system synchronize their frame delivery to the reference signal received on the board's black burst input.

To enable Genlock SDI:

1. Connect a blackburst or tri-level sync source to the black burst input on the Deltacast SDI board. Every node carrying SDI outputs that should run in lockstep must receive the same reference signal.
2. Open Show Properties (Preferences).
3. Enable the Genlock SDI toggle.

Genlock keeps all Runner nodes with SDI outputs scanning out in step — needed for multi-projector arrays, LED walls, and broadcast environments where downstream equipment expects time-aligned signals.

Genlock and content timing

Genlock aligns the SDI signal — every output scans out in phase. It does not control which frame of content each node shows. That timing still comes from NTP. Two genlocked nodes can therefore land one frame apart when their NTP timestamps round to different frame numbers: the signals are in phase, but the content is a frame off.

To lock the content as well, combine genlock with GPU hardware sync (Hardware Sync Groups). The framelock frame count then drives playback timing in place of NTP. Every node then presents the same frame.

Frame Delay

The Delay Frames setting (0–10 frames) adds a configurable output delay to the display. Each frame of delay adds one additional frame buffer to the rendering pipeline before the pixels are sent to the SDI output.

This is useful for compensating processing latency in downstream equipment. For example, if an LED processor introduces a fixed two-frame delay, you can add a matching delay to other displays in the system so that all outputs appear synchronized to the viewer.

The delay buffer is allocated at initialization — the SDI output always maintains (delay + 1) render target buffers in a ring, presenting the oldest completed frame while rendering into the newest.

Hardware Requirements

SDI output in WATCHOUT requires a Deltacast SDI capture/output card installed in the Runner node, paired with a GPU that supports zero-copy transfers from the render pipeline into the card.

Key requirements:

• Deltacast SDI card with output capability (e.g. Deltacast DELTA-12G series or equivalent).
• Deltacast drivers installed on the Runner node. The driver package ships with the runtime libraries WATCHOUT needs — no separate SDK install is required.
• Professional NVIDIA GPU with GPUDirect support (Quadro / RTX A-series / RTX Ada Generation, etc.). GPUDirect enables direct-DMA transfers between the GPU framebuffer and the SDI card, avoiding a round-trip through system memory. Consumer NVIDIA cards and non-NVIDIA GPUs do not support GPUDirect and cannot drive SDI output.

If the Deltacast driver is not loaded, the Runner logs an error and the SDI display does not initialize. Verify that the driver is installed and the card is recognized by the operating system before configuring SDI outputs.

Related

• ST 2110 Video Over IP — the IP-based alternative to SDI, also through a Deltacast board.
• Setting Up ST 2110 — commissioning an ST 2110 output if you choose IP instead of SDI.

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