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Documentation Index

Fetch the complete documentation index at: https://docs.streampixel.io/llms.txt

Use this file to discover all available pages before exploring further.

This page covers how the SDK selects video codecs, the resolution presets it supports, the available resolution modes, and the bitrate and quality controls.

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Supported codecs

The SDK supports four video codecs:
CodecBrowser SupportNotes
H264All browsersDefault fallback, widest compatibility
VP8All browsersGood compatibility
VP9Chrome, Edge, FirefoxBetter compression than VP8
AV1Chrome, EdgeBest compression. Requires Unreal Engine 5.3+ and is not supported on Firefox
AV1 requires Unreal Engine 5.3 or later and is not supported on Firefox. On older UE versions or unsupported browsers, the SDK will fall back automatically — but you should plan your codec preferences accordingly.

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Codec negotiation

The SDK automatically negotiates the best codec:
  1. Detects which codecs the browser supports via RTCRtpReceiver.getCapabilities('video')
  2. Tries the primaryCodec you configured (or dashboard default)
  3. If the primary codec is unavailable or incompatible:
    • Tries the fallBackCodec
  4. If the fallback is also unavailable:
    • Falls back to H264
H264 is the ultimate fallback. If both your primary and fallback codecs are unavailable, the SDK will always fall back to H264 — so every user will get a working stream regardless of browser.
Special rules:
  • AV1 requires Unreal Engine version > 5.3. On older versions, it falls back automatically.
  • Firefox does not support setting codec preferences via the setOptionSettingOptions API. The SDK handles this silently.
await StreamPixelApplication({
  appId: 'your-project-id',
  primaryCodec: 'AV1',
  fallBackCodec: 'H264',
});

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Resolution presets

The SDK uses predefined resolution presets:
PresetDimensions
"360p (640x360)"640 x 360
"480p (854x480)"854 x 480
"720p (1280x720)"1280 x 720
"1080p (1920x1080)"1920 x 1080
"1440p (2560x1440)"2560 x 1440
"4K (3840x2160)"3840 x 2160

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Device-specific resolution

The SDK detects the user’s device and applies the appropriate starting resolution:
DeviceConfig ParameterDefault
DesktopstartResolution"1080p (1920x1080)"
TabletstartResolutionTab"720p (1280x720)"
MobilestartResolutionMobile"480p (854x480)"
Device detection uses the browser’s user agent string.

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Resolution modes

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Fixed Resolution Mode

Sends the exact resolution dimensions to UE. The stream always renders at the specified resolution regardless of the browser viewport size.
Fixed Resolution Mode is the simplest option and works well for most use cases. If you don’t need the stream to adapt to different viewport sizes, start here.

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Dynamic Resolution Mode

Adapts the resolution to match the browser viewport while respecting the maxStreamQuality ceiling. When the viewport is smaller than the max quality, the SDK sends viewport dimensions. When larger, it scales down proportionally. In this mode, the SDK also listens for window resize events and adjusts resolution automatically (with a 200ms debounce).

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Crop on Resize Mode

Similar to Dynamic Resolution Mode but preserves the aspect ratio by scaling to fit the viewport with proportional dimensions.

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Changing resolution at runtime

Use UIControl.handleResMax() to change the maximum resolution during a session: 
UIControl.handleResMax('1920x1080');
UIControl.handleResMax('1280x720');
The format is "WIDTHxHEIGHT". In Fixed Resolution Mode, this sends a r.SetRes console command to UE. In Dynamic/Crop modes, it recalculates the resolution based on the viewport.

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Bitrate control

ParameterTypeDefaultDescription
minBitratenumber1Minimum bitrate in Mbps
maxBitratenumber100Maximum bitrate in Mbps

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Quantization parameter (QP)

QP controls video compression quality. Lower values mean better quality but more bandwidth.
ParameterTypeDefaultDescription
minQPnumber20Minimum QP (1-51, lower = better quality)
maxQPnumber-1Maximum QP (-1 = no limit / auto)

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Next steps

Initialization and configuration

See all configuration parameters in one place.

Input controls

Configure mouse, keyboard, touch, gamepad, and WebXR input.