How to set up a video processor / scaler for an LED wall

A video processor (sometimes called a scaler, sender, or LED controller) sits between playback and the receiving cards. It accepts HDMI, SDI, or ST 2110, builds a canvas the size of your wall, and ships packets over Ethernet or fiber. If the canvas is wrong, every other department looks incompetent: lyrics are soft, IMAG is cropped, and the “dead” column is actually unmapped.

This tutorial is manufacturer-neutral. Menu names differ between sending-card families, but the job is the same: define the wall, lock the input, choose how mismatched signals fit, and document a fallback.

Understand the three resolutions in play

Every show has at least three numbers:

1. Source resolution — what ProPresenter, a media server, or a switcher emits (often 1920×1080 or 3840×2160).
2. Processor canvas — the pixel map the processor believes is the LED wall.
3. Wall native resolution — columns × cabinet pixels, from the layout tutorial.

When all three match, life is simple. They rarely match. Your job is to pick where the conversion happens.

Best case: canvas equals wall native. The source is built at that size, or the processor scales 1080p/4K onto that canvas with a known crop.

Acceptable: canvas is a standard 16:9 (1920×1080) and the wall is close. You will pillarbox, letterbox, or slightly stretch. Decide which, do not leave “auto.”

Painful: canvas is 1920×1080, the wall is 2016×1152, and someone enabled “full screen” stretch. Circles become ovals and the IMAG operator gets blamed.

Write the three numbers on a label on the processor and in the show file.

Physical hookup that does not bite you later

1. Power the processor from a clean, preferably UPS-backed circuit. A reboot mid-service is a black wall.
2. Connect program video with a cable you can replace in the dark: SDI for long copper runs, HDMI only for short, locked-down runs, fiber or NDI/ST 2110 when the plot demands it.
3. If the processor has a dedicated program and preview input, use them. Do not daisy-chain a cheap HDMI splitter as your only redundancy.
4. Connect output Ethernet or fiber to the first receiving-card chain. Label port 1 as the same port you will map in software.
5. Genlock or house sync if cameras and IMAG must stay in time. Unsynchronized processors can produce tearing that looks like a bad cabinet.

Disable consumer “auto input” hopping if the unit has it. A laptop that wakes on HDMI 2 should not steal Sunday’s program.

Set EDID and input timing on purpose

EDID is how the processor tells the playback computer “I am a 1920×1080 display at 59.94 Hz.” If EDID is wrong, macOS and Windows will output 4K, 30 Hz, or a 16:10 desktop that the scaler then wrecks.

Procedure:

1. Set the processor input preferred format to the format you actually want (example: 1920×1080p59.94, or the wall-native timing if the sender allows a custom EDID).
2. Apply / burn EDID to that input.
3. Hot-plug or restart the playback machine so it rereads EDID.
4. Confirm the processor status page shows a locked signal at the expected rate — not 60.00 when the house is 59.94, and not 30 Hz “to save bandwidth.”

Churches that mix IMAG often standardize on 59.94 to match US cameras. A 60.00 laptop on a 59.94 house will eventually drift or stutter. Match the house.

If you must ingest 4K into a 1080-class wall, let the processor downscale on a dedicated 4K input rather than trusting a $20 HDMI converter.

Build the canvas and the output mapping

Create a canvas equal to the wall’s native pixels, or a documented 16:9 stand-in. Then place input layers on that canvas.

Typical layer choices:

• Full canvas, keep aspect — 1080p sits in the middle of a wider wall with even side bars. Good default.
• Full canvas, fill — crops the top/bottom or sides. Use when you would rather lose picture than see bars.
• Pixel-to-pixel — source equals canvas. No scaler. Sharpest. Requires matching templates.
• Multiple layers — IMAG in a window, lyrics in a lower third band, scenic on the sides. This is how many houses actually run.

Disable any “overscan” or “TV” mode. LED walls want the entire raster.

If the processor supports output groups (one canvas feeding several sending cards), keep each group’s port list identical to the receiving-card map. A canvas that is 2016 pixels wide but only 1920 pixels mapped will leave a dark strip that techs chase as a “failed column.”

Save the project to internal memory and export a file to a USB drive or the house NAS. Name it with the date and wall size: Sanctuary_2016x1152_2026-04-12.

Scaling, bit depth, and color

Set the scaler to a high-quality filter for lyrics (they need sharp edges) and verify chroma sampling. If the source is 4:2:2 SDI and the processor is set to treat it as RGB with the wrong color range, blacks crush or look milky.

Check:

• Color range: Limited vs full. HDMI from a computer is often full range; SDI cameras are limited. A mismatch looks like a bad calibration.
• Color space: Rec. 709 is the safe house default unless you have an HDR pipeline you actually understand.
• Bit depth: 8-bit is common; 10-bit helps gradients on fine-pitch indoor walls.
• Low latency mode: Enable for IMAG and IMAG-plus-lyrics if the unit offers it. Disable extra frames of “motion smoothing.”

Test with a circle, a 1-pixel grid, and a real lyric slide. Geometry errors show up on circles. Softness shows up on type.

Backup inputs and failovers

Design a failure that is boring:

• Program on SDI 1 from the switcher.
• Backup on HDMI or SDI 2 from a second ProPresenter machine or a still-store.
• A labeled “BLACK / LOGO” still on an internal layer you can recall if both computers die.

Know which button takes the wall to an internal logo in under three seconds. Practice it. A processor with a beautiful canvas and no documented backup is not finished.

If the unit supports input backup (automatic switch on signal loss), test it by pulling the program cable during rehearsal — not during the first song.

Sync, test patterns, and a walk-the-wall

After mapping receiving cards (see the next tutorial), use the processor’s test patterns:

1. Color bars or a solid red / green / blue to find swapped modules.
2. Grid or numbered cabinets to confirm the map origin.
3. Moving ramp to expose tearing and dropped packets.
4. Real program at show brightness, not shop brightness.

Walk the wall with a radio. The person at the processor should be able to flash a single cabinet or a single output port. If they cannot, you do not yet have control — you have a hope.

Common mistakes

Auto everything. Auto input, auto EDID, auto scale. It works on the bench and fails when a guest laptop appears.

Canvas copied from last weekend’s rental. Old 1536×768 settings on a new 2016×1152 house wall produce a tiny picture in the corner or a stretched mess.

HDMI as the only program path on a 30 m run. Use SDI or fiber. HDMI extenders fail in interesting ways.

Ignoring frame rate. 30 Hz IMAG on LED looks cheap. 24 fps film looks like film until someone puts lyrics on it.

Two operators scaling. ProPresenter scales to 1920×1080, the processor scales again to the wall. Pick one scaler when you can.

No UPS. A 20 ms blink on house power becomes a 40-second processor boot.

Commissioning checklist

• Wall native resolution documented
• Canvas matches native or a written 16:9 plan
• EDID burned; playback machine locked to the right timing
• Color range and 709 confirmed with a test pattern
• Program and backup inputs labeled and tested
• Project saved internally and exported
• Test patterns walked on the real wall
• Someone besides you can recall the backup still

When the processor is honest about the canvas, mapping and playback become ordinary work instead of folklore.