TL;DR
Backend metrics can't see rebuffering, slow startups, or failed plays; those happen inside the player. We'll instrument an HTML5/hls.js player to capture real QoE signals in ~40 lines, look at what the numbers mean, and then be honest about where DIY telemetry stops scaling and what the managed options cost.
The incident that teaches everyone this lesson
A user writes in: "the video keeps stopping." You check Grafana. Origin 5xx: flat zero. CDN hit ratio: healthy. Uptime: perfect. You close the ticket as "cannot reproduce," and next week there are four more.
Nothing is lying. Your dashboards describe the server side of the socket, and playback quality is a client-side phenomenon. Here's the mismatch in table form:
