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Overview

The host.capture section configures Windows Graphics Capture (WGC) for screen capture, including GPU texture copying, frame queuing, adaptive backoff, and thread priority optimization.

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Texture Copy Pool

GPU texture copy operations require pre-allocated D3D11 resources.
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capture.copyPoolSize
integer
default:"4"
Number of D3D11 texture copy resources in the pool.Default: 4Higher values allow more parallel copy operations but use more GPU memory.Recommended:
  • 4 - Standard (default)
  • 6-8 - High frame rate (120+ FPS)
  • 2-3 - Memory constrained systems
Increase this if you see frame drops at high frame rates.
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capture.framePoolBuffers
integer
default:"2"
Number of frame buffers for WGC capture.Default: 2Minimum of 2 required for double-buffering. Higher values add latency.

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Frame Queue Management

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capture.maxQueueDepth
integer
default:"2"
Maximum frames queued for encoding.Default: 2Lower values reduce latency but may cause frame drops if encoder is slow.Recommended:
  • 1 - Absolute minimum latency (may drop frames)
  • 2 - Low latency (default)
  • 3-4 - More stable, slightly higher latency
Values above 3 significantly increase latency. Only use for debugging.
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capture.dropWindowMs
integer
default:"500"
Time window in milliseconds for frame drop detection.Default: 500 msUsed to detect sustained frame dropping vs. occasional drops.
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capture.dropMinEvents
integer
default:"12"
Minimum frame drops within window to trigger warnings.Default: 12Prevents spurious warnings from occasional frame drops.

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Cursor and Border

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capture.cursor
boolean
default:"false"
Render cursor into captured frames.Default: falseWhen disabled, the client renders its own cursor for lower latency.
Keep disabled for better cursor responsiveness. Enable only if client-side cursor has issues.
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capture.borderRequired
boolean
default:"false"
Require window border for capture.Default: falseWhen enabled, WGC only captures windows with borders (excludes fullscreen exclusive).

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Frame Change Detection

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capture.skipUnchanged
boolean
default:"true"
Skip encoding frames identical to previous frame.Default: trueSaves bandwidth and GPU cycles when screen content is static.
Keep enabled unless you need constant frame output for testing.
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capture.minUpdateInterval100ns
integer
default:"166666"
Minimum frame capture interval in 100-nanosecond units.Default: 166666 (16.67 ms = 60 FPS)Controls the maximum capture rate. For 60 FPS: 1000000 / 60 * 10 = 166666Common values:
  • 83333 - 120 FPS
  • 166666 - 60 FPS (default)
  • 333333 - 30 FPS

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Adaptive Backoff

Dynamically reduce capture rate when encoder falls behind.
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capture.adaptiveBackoff
boolean
default:"false"
Enable adaptive capture rate backoff.Default: falseWhen enabled, automatically reduces capture rate if encoder cannot keep up.
This adds complexity and may cause stuttering. Only enable if experiencing consistent encoder saturation.
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capture.adaptiveWindowMs
integer
default:"2000"
Time window for adaptive backoff measurements.Default: 2000 msLonger windows provide more stable adaptation but slower response.
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capture.adaptiveEagainThreshold
integer
default:"8"
Number of EAGAIN (encoder busy) errors to trigger backoff.Default: 8Higher values tolerate more encoder saturation before reducing capture rate.

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Thread Priority (MMCSS)

Multimedia Class Scheduler Service (MMCSS) provides real-time thread priority for capture.
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capture.mmcss.enable
boolean
default:"true"
Enable MMCSS for capture thread.Default: trueBoosts capture thread priority to reduce jitter and frame timing variance.
Keep enabled for consistent frame timing and lowest latency.
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capture.mmcss.priority
integer
default:"4"
MMCSS task priority level.Default: 4Range: 1 (lowest) to 8 (highest)Higher values give more CPU priority but may impact other system tasks.Recommended:
  • 3-4 - Standard priority (default)
  • 5-6 - High priority (gaming)
  • 7-8 - Maximum priority (use with caution)

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Windows Graphics Capture (WGC)

WGC is the modern Windows 10+ screen capture API. Configuration is primarily done through the parameters above.

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How WGC Works

  1. Capture: WGC provides GPU texture from compositor
  2. Copy: Texture copied to staging resource from copyPoolSize pool
  3. Queue: Frame queued for encoding (up to maxQueueDepth)
  4. Encode: FFmpeg/NVENC encodes the frame
  5. Stream: Encoded frame sent over WebRTC

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WGC Requirements

  • Windows 10 version 1903 or later
  • DirectX 11 compatible GPU
  • Target window must be visible (minimized windows cannot be captured)
WGC cannot capture UAC prompts, secure desktop, or some protected content (DRM).

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Performance Optimization

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Low Latency Configuration

Minimize every source of latency: 
{
  "capture": {
    "copyPoolSize": 3,
    "maxQueueDepth": 1,
    "framePoolBuffers": 2,
    "cursor": false,
    "skipUnchanged": true,
    "minUpdateInterval100ns": 83333,
    "adaptiveBackoff": false,
    "mmcss": {
      "enable": true,
      "priority": 6
    }
  }
}
Setting maxQueueDepth to 1 provides minimum latency but may drop frames if encoding cannot maintain target frame rate.

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High Frame Rate Configuration

For 120+ FPS capture: 
{
  "capture": {
    "copyPoolSize": 8,
    "maxQueueDepth": 2,
    "framePoolBuffers": 3,
    "cursor": false,
    "skipUnchanged": true,
    "minUpdateInterval100ns": 83333,
    "mmcss": {
      "enable": true,
      "priority": 7
    }
  }
}

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Stable Configuration

For consistent performance with minimal frame drops: 
{
  "capture": {
    "copyPoolSize": 6,
    "maxQueueDepth": 3,
    "framePoolBuffers": 2,
    "cursor": false,
    "skipUnchanged": true,
    "adaptiveBackoff": true,
    "adaptiveWindowMs": 1000,
    "mmcss": {
      "enable": true,
      "priority": 4
    }
  }
}

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Troubleshooting

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Frame Drops

Symptoms: Frequent frame drops, stuttering Solutions:
  1. Increase copyPoolSize to 6-8
  2. Increase maxQueueDepth to 3-4
  3. Enable adaptiveBackoff
  4. Reduce target fps in video configuration
  5. Use faster NVENC preset (p1 or p2)

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High Latency

Symptoms: Delayed response to inputs Solutions:
  1. Reduce maxQueueDepth to 1-2
  2. Disable adaptiveBackoff
  3. Set cursor to false
  4. Ensure mmcss.enable is true
  5. Increase mmcss.priority to 6-7

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GPU Memory Issues

Symptoms: Crashes, D3D11 errors Solutions:
  1. Reduce copyPoolSize to 2-3
  2. Reduce framePoolBuffers to 2
  3. Lower capture resolution
  4. Check GPU memory usage with Task Manager

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CPU Usage

Symptoms: High CPU usage in capture thread Solutions:
  1. Enable skipUnchanged
  2. Use hardware encoding (NVENC/QSV/AMF)
  3. Increase minUpdateInterval100ns to reduce frame rate
  4. Disable gpuTiming if enabled

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Example: Gaming Streaming Profile

{
  "capture": {
    "copyPoolSize": 6,
    "maxQueueDepth": 2,
    "framePoolBuffers": 2,
    "dropWindowMs": 500,
    "dropMinEvents": 12,
    "mmcss": {
      "enable": true,
      "priority": 6
    },
    "cursor": false,
    "borderRequired": false,
    "minUpdateInterval100ns": 83333,
    "skipUnchanged": true,
    "adaptiveBackoff": false
  }
}
This configuration provides:
  • 120 FPS capture capability
  • Low latency (2 frame queue depth)
  • High thread priority
  • Efficient bandwidth usage (skip unchanged frames)
  • Sufficient copy pool for smooth operation

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