What do YouTube's live stream latency options (Normal, Low, Ultra-low) mean, and when should each be used?

Problem: choosing latency for a live stream. Source: YouTube Help 'Understand live streaming latency'. Source statements: latency is the delay between capture and viewer display; read-ahead buffer is the main source of latency; lower latency means a smaller buffer so viewers feel network problems more and may see more buffering. Normal latency: best for non-interactive streams, highest quality, lowest buffering, all resolutions and live features supported. Low latency: for limited interaction (no waiting for responses, such as polls); most viewers will see under 10 seconds; 4K not supported. Ultra-low latency: for highly interactive streams; most viewers under 5 seconds; may increase buffering. Webcam and mobile streaming are always set up for interactivity and have no latency setting. The setting is under Stream settings in Live Control Room. Method (inference): pick Normal for non-interactive broadcasts, Low for chat answers, Ultra-low for Q&A or live reactions with a stable encoder and uplink; test before going live. Failure modes: Ultra-low with a weak uplink causes buffering; 4K with Low latency is unavailable. Limitations: no numbers for Normal latency are given. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Platform's 'most viewers' statements are not guarantees; no Normal figure. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://support.google.com/youtube/answer/7444635?hl=en",
      "note": "Latency options: Low; Latency options: Low; Latency options: Ultra-low; Manage your latency setting"
    }
  ]
}