kit-app-streaming-debug

par nvidia

Utiliser lors de l'investigation des goulots d'étranglement de performance du livestream de l'application Kit, des latences WebRTC/natives StreamSDK, des blocages, des images perdues, des statistiques WebRTC du navigateur, de la barrière de copie…

npx skills add https://github.com/nvidia/omniperf --skill kit-app-streaming-debug

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Kit App Streaming Debug

Debug Kit livestream performance end-to-end before jumping into generic profiling. Always collect both server-side Kit logs and browser-side WebRTC evidence, then correlate by timestamp around the lag/freeze event.

Collect Kit Evidence

Run the Kit app with StreamSDK event tracing and verbose file logs. Keep --no-window for app-stream tests when resolution mismatch is suspected.

# Windows
.\repo.bat launch -- --no-window --/exts/omni.kit.livestream.app/primaryStream/enableEventTracing=true --/log/channels/omni.kit.livestream.streamsdk=verbose --/log/fileLogLevel=verbose

# Linux
./repo.sh launch -- --no-window --/exts/omni.kit.livestream.app/primaryStream/enableEventTracing=true --/log/channels/omni.kit.livestream.streamsdk=verbose --/log/fileLogLevel=verbose

If extension context is needed, also enable:

--/log/channels/omni.kit.livestream.webrtc=verbose
--/log/channels/omni.kit.livestream.app=verbose

Extract the known streaming failure markers:

rg -n -C 3 "Timeout of [0-9]+ms exceeded waiting for copy fence|Cannot stream video frame because the video stream is not connected|Still cannot stream video frame|Cannot stream video frame with resolution|NVST_R_BUSY|Client disconnected from WebRTC server" path/to/kit.log

Interpret them this way:

Marker	Likely cause	Next check
`Timeout of 1000ms exceeded waiting for copy fence`	Renderer/GPU stall before the framebuffer copy completes	Correlate with frame time, GPU utilization, and Tracy/NSight render zones
`Cannot stream video frame because the video stream is not connected`	WebRTC session has not established, or video stream dropped	Check browser ICE state, connection events, and nearby disconnect logs
`Still cannot stream video frame...`	Connection did not recover inside the wait timeout, frame dropped	Treat as stream/session instability, not render cost by itself
`Cannot stream video frame with resolution ... differs...`	OS/window resize or AOV/render resolution changed after connect	Try `--no-window`, fixed resolution, disable viewport fill behavior, or use dynamic resize only if required
`NVST_R_BUSY`	StreamSDK is not accepting frames fast enough	If not adjacent to disconnect/reconnect, suspect encoder, network, or client backpressure
`Client disconnected from WebRTC server`	Client/session dropped	Align with browser ICE/NACK/PLI/freeze events

Collect Browser Evidence

Open chrome://webrtc-internals before connecting to the stream. After a lag event, use Create dump and inspect packet loss, jitter, frames dropped, decode time, bitrate, freezes, NACK/PLI, and the selected ICE candidate pair.

For ~/proj/ov-web-rtc, run the dev client with npm run dev and capture console logs. Add or inspect an onStreamStats callback like:

onStreamStats: (message: StatsEvent) => {
  const s = message.data.stats;
  console.table({
    fps: s.fps,
    rtdMs: s.rtd,
    decodeMs: s.avgDecodeTime,
    frameLoss: s.frameLoss,
    packetLoss: s.packetLoss,
    bandwidthMbps: s.totalBandwidth,
    bitrateMbps: s.currentBitrate,
    utilizedPct: s.utilizedBandwidth,
    resolution: `${s.streamingResolutionWidth}x${s.streamingResolutionHeight}`,
    codec: s.codec,
  });
}

Browser-side interpretation:

Symptom	Likely bottleneck
High `avgDecodeTime`, low packet loss	Client decode/GPU/display bottleneck
High `packetLoss`, `frameLoss`, NACK/PLI, jitter, or freezes	Network or congestion problem
`utilizedBandwidth` near 100%, bitrate near/above available bandwidth	Bandwidth cap or congestion control
Low browser FPS with clean browser stats but Kit copy-fence/NVST warnings	Server render/copy/encoder/backpressure
Browser resolution differs from expected Kit stream resolution	Resize/configuration mismatch

Profiling Follow-Up

Use Tracy only after logs indicate the server side is involved. Add the profiling args to the same Kit run:

--/app/profilerBackend=tracy --/app/profileFromStart=true --/profiler/gpu/tracyInject/enabled=true --/app/profilerMask=1 --/plugins/carb.profiler-tracy.plugin/fibersAsThreads=false --/profiler/channels/carb.events/enabled=false --/profiler/channels/carb.tasking/enabled=false --/rtx/addTileGpuAnnotations=true --/profiler/enabled=true --/profiler/gpu=true --enable omni.kit.profiler.window

Use the profiling skill for capture mechanics and nsys-analyze for trace analysis. Do not promise StreamSDK-internal zones when StreamSDK source is unavailable; correlate log timestamps with surrounding Kit zones such as SharedFrameBuffer::waitForCopy, SharedFrameBuffer::streamBuffer, render zones, and frame markers.

Report Shape

Summarize:

Kit run args and log path.
Browser artifacts: console stats and webrtc-internals dump.
Timeline around the lag event.
Matched markers and likely bottleneck category: renderer/GPU, session/network, resize/config, StreamSDK/encoder backpressure, or client decode.
Next action: config fix, network/client investigation, or server-side profiling.

Source references in this workspace: ~/proj/kit-livestream for omni.kit.livestream.app and omni.kit.livestream.webrtc; ~/proj/ov-web-rtc for browser stats and dev client logging.