# Passthrough Capture Card Guide

## Capture Card — Passthrough Method

This is the simplest capture card setup. The HDMI signal from your Gaming PC passes *through* the capture card on the way to your monitor — no OBS, no projector, no extra software on the Gaming PC. The capture card sits in between and copies the signal to the Script PC.

> **Tradeoff:** Passthrough is simpler but **your gaming resolution and refresh rate are limited to what the capture card supports.** If your capture card maxes out at 1080p 240Hz, that's what your monitor gets too. If you play at higher resolutions (1440p, 4K) or higher refresh rates (360Hz+), use the OBS Projector Method instead — it decouples your gaming display from the capture card entirely.

#### When to Use Passthrough

* You play at **1080p natively** and your capture card supports 1080p @ 240Hz passthrough — this is the ideal passthrough scenario.
* You're using a **USB capture card** (like the Elgato 4K X) and don't want to deal with OBS setup.
* You want the **simplest possible setup** and are okay matching your gaming resolution to the capture card's limits.

#### When to Use OBS Projector Instead

* You play at **1440p, 4K, or refresh rates above what your capture card supports** (e.g., 1440p 360Hz) and don't want to downgrade.
* You want **maximum flexibility** — OBS Projector lets you game at any resolution while the capture card receives a clean 1080p 240Hz signal independently.

***

### Prerequisites

#### Capture Card Requirements

The same hardware requirements apply as with OBS Projector — not all capture cards work well for this use case.

**What you need:**

* A capture card that supports **1080p @ 240 FPS passthrough** (the passthrough spec, not just the capture spec)
* **NV12** color format support
* Low latency — cheap generic cards from Amazon often run at 50–60 FPS with high latency

**Recommended cards:**

* **Elgato 4K Pro** (PCIe) — lowest latency, best option if your Script PC has a PCIe slot
* **Elgato 4K X** (USB) — very close performance, requires **USB 3.1/3.2 Gen 2** port
* **AVerMedia GC573 / GC553G2** — solid alternatives

> **Check the passthrough spec specifically.** Some capture cards can *capture* at 1080p 240Hz but only *passthrough* at lower specs. Verify both.

> **USB-C doesn't mean Gen 2.** If using a USB capture card, confirm the port is actually Gen 2. On a Gen 1 port, you're limited to \~120 FPS capture regardless of what the card supports.

> **PCIe slot bandwidth matters.** PCIe x1 slots can be bandwidth-limited. If capture FPS is lower than expected, try a different slot or check your motherboard manual.

***

### Step 1: Install the Capture Card (Script PC)

The capture card goes in the **Script PC** — not the Gaming PC.

1. Install the card in the Script PC's PCIe slot (or connect via USB).
2. **Update the firmware** from the Script PC. Visit the manufacturer's support page ([Elgato](https://www.elgato.com/downloads) / [AVerMedia](https://www.avermedia.com/support) / [Magewell](https://www.magewell.com/downloads)) for firmware tools and drivers.
3. **Reboot the Script PC** before continuing.

***

### Step 2: Connect the Hardware

This is the key difference from the OBS Projector method — the signal goes *through* the capture card.

1. Connect an **HDMI cable** from your **Gaming PC GPU output** → **HDMI IN** on the capture card (installed in the Script PC).
2. Connect an **HDMI cable** from the **HDMI OUT** on the capture card → **your gaming monitor**.

Your gaming monitor now receives the signal after it passes through the capture card. The capture card copies the signal and makes it available to the Script PC simultaneously.

> **No second HDMI output needed on the GPU.** Unlike the OBS Projector method, passthrough only uses one GPU output — the capture card sits in line between the GPU and your monitor.

***

### Step 3: Verify the Signal

At this point, your gaming monitor should display normally through the capture card. If the monitor is black or the signal looks wrong:

1. Check that HDMI cables are in the correct ports — **GPU out → card IN**, **card OUT → monitor**.
2. Try a different HDMI cable. Passthrough at high refresh rates requires good cables (HDMI 2.0+ for 1080p 240Hz).
3. Make sure the capture card is powered and recognized by the Script PC.

Your Gaming PC doesn't need any additional software for passthrough. No OBS, no display settings changes, no projector setup. The capture card handles everything in hardware.

***

### Step 4: Configure the Application (Script PC)

1. Set **Capture Mode** to **Capture Card** in the capture tab.
2. Select the correct capture source/device. If you see your webcam instead of the game feed, cycle through device indices (device 0, device 1, etc.) until the game appears.
3. Set the capture format. We recommend **1080p NV12** at the highest FPS your card supports (ideally 240). If 1080p isn't available, try **720p** — it'll work with slightly less detection accuracy at range.
4. Load a community config set to capture card mode.
5. Press Start. The debug window should show the live game feed.

> **720p vs 1080p:** 1080p gives better detection accuracy at longer distances since targets have more pixels. 720p uses less processing power and can result in slightly lower latency. For most setups, 1080p is the better choice unless your Script PC is struggling with performance.

> **Make sure no other apps are using the capture card.** Close any other software that might access the capture device (Elgato software, camera apps, streaming tools) on the Script PC before starting. Having another app open on the capture card can block access.

***

### Troubleshooting

#### Game is zoomed in or resolution looks wrong on passthrough

This happens when the capture card's passthrough resolution doesn't match your game's expected resolution. Make sure your game is set to the same resolution that the capture card passes through (e.g., if the card passes through 1080p, your game should be set to 1080p). If your game is set to a resolution the card can't passthrough, the display may appear zoomed or distorted.

If you want to play at a higher resolution than your capture card supports passthrough for, switch to the OBS Projector Method instead.

#### Low capture FPS

**1. Check capture format.** In the application's capture settings, make sure you're set to NV12 at the highest resolution/FPS combo your card supports. If NV12 isn't available for your card, try YUY2.

**2. USB card on wrong port.** USB capture cards need a Gen 2 port for full speed. On Gen 1 you'll be stuck around 120 FPS.

**3. PCIe slot bandwidth.** Try a different PCIe slot if FPS is unexpectedly low.

**4. Cheap card limitations.** Generic cards often max at 50–60 FPS regardless of settings. If your card can't do 1080p 240 NV12, it may not be suitable for this use case — "streaming and 2pc AI are very different workloads."

#### Webcam showing instead of game feed

Wrong capture device selected. Change the device index in the capture settings. If no device shows the game, the capture card isn't being recognized — check physical connections and firmware/drivers.

#### Capture backend issues

The application offers different capture backends: `opencv`, `ffmpeg`, and `libav`. If one causes problems (low FPS, freezing), try the others — stop, switch, then start again.

#### Stuttery aim despite high capture FPS

Check all three metrics in the debug view separately:

* **Capture FPS** — frames from the capture card (should match your card's capabilities)
* **Detection FPS** — how fast the model processes frames (bottleneck is Script PC GPU/model)
* **Debug display FPS** — just the visual display (cap this at 60 FPS with scale 0.5 to save resources)

If capture FPS is fine but detection FPS is low, the bottleneck is your Script PC, not the capture card.

***

### Quick Reference

| Setting                   | Value                                     |
| ------------------------- | ----------------------------------------- |
| Capture card installed in | Script PC (PCIe slot or USB Gen 2)        |
| HDMI cable 1              | Gaming PC GPU out → Capture card HDMI IN  |
| HDMI cable 2              | Capture card HDMI OUT → Gaming monitor    |
| Gaming PC software        | None required                             |
| App Capture Mode          | Capture Card                              |
| App Capture Format        | 1080p NV12 @ 240 FPS (recommended)        |
| Fallback format           | 720p NV12 (lower accuracy, lower latency) |


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