How does Unity Recorder accumulate path-tracing samples, how do I get clean frames without motion blur, and why do frames come out overexposed?

Problem. Path-traced HDRP frames are noisy until sub-samples converge. Conditions. HDRP with ray tracing set up and a path tracing override in the scene; path-tracing accumulation requires DX12 (Recorder 5.1.7 docs). Method. Samples is the number of sub-frames per frame and each sub-frame captures one path-tracing sample. With Shutter Interval above 0, samples are accumulated only inside the interval and the Shutter Profile weights them; with Interval 0 time does not advance, Shutter Profile is not applied, and all Samples converge one static moment (no blur). If noisy, raise Samples. Failure modes. With automatic Exposure and Adaptation set to Progressive, exposure is re-evaluated each sub-frame and noisy early sub-frames can overexpose the result; set Exposure Adaptation Mode to Fixed. A short Shutter Interval reduces path-tracing samples accumulated; the documented workaround is to disable path-tracing overrides on volumes. Limitations. HDRP path-tracing limitations also apply. Version/date. Recorder 5.1.7 docs, fetched 2026-10-24. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Docs give no sample counts or noise measurements; how many Samples are enough is scene-dependent and untested here. Docs themselves are partly inconsistent on whether to raise Samples or disable overrides for noise. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://docs.unity3d.com/Packages/com.unity.recorder@5.1/manual/RecordingAccumulationPathTracing.html",
      "note": "Configure path-tracing accumulation without motion blur; Known issues: overexposed frames; Known issues: path tracing with motion blur"
    },
    {
      "url": "https://docs.unity3d.com/Packages/com.unity.recorder@5.1/manual/KnownIssues.html",
      "note": "Configure path-tracing accumulation without motion blur; Known issues: overexposed frames; Known issues: path tracing with motion blur"
    }
  ]
}