From c3b3c606dbd30565c46af5ee49bdde9d73fbf95b Mon Sep 17 00:00:00 2001
From: mkelvers <mikkelelvers@outlook.com>
Date: Tue, 16 Jun 2026 01:34:42 +0200
Subject: [PATCH] feat: profile hls playback

---
 static/player/hls_profile.ts | 115 +++++++++++++++++++++++++++++++++++
 static/player/video.ts       |   5 ++
 2 files changed, 120 insertions(+)
 create mode 100644 static/player/hls_profile.ts

diff --git a/static/player/hls_profile.ts b/static/player/hls_profile.ts
new file mode 100644
index 0000000..10ac32a
--- /dev/null
+++ b/static/player/hls_profile.ts
@@ -0,0 +1,115 @@
+import Hls from "hls.js";
+import type { ErrorData } from "hls.js";
+
+interface HLSPlaybackProfile {
+  sourceLoads: number;
+  manifestParsed: number;
+  stalls: number;
+  totalStallMs: number;
+  seeks: number;
+  totalSeekMs: number;
+  errors: number;
+  fatalErrors: number;
+  lastErrorType: string;
+}
+
+declare global {
+  interface Window {
+    __malHlsProfile?: HLSPlaybackProfile;
+  }
+}
+
+const createProfile = (): HLSPlaybackProfile => ({
+  sourceLoads: 0,
+  manifestParsed: 0,
+  stalls: 0,
+  totalStallMs: 0,
+  seeks: 0,
+  totalSeekMs: 0,
+  errors: 0,
+  fatalErrors: 0,
+  lastErrorType: "",
+});
+
+const mark = (name: string): void => {
+  performance.mark(`mal.hls.${name}`);
+};
+
+const measure = (name: string, startMark: string): void => {
+  try {
+    performance.measure(`mal.hls.${name}`, `mal.hls.${startMark}`);
+  } catch {
+    // Missing marks can happen if HLS.js emits a later event after cleanup.
+  }
+};
+
+export const attachHLSProfile = (hls: Hls, video: HTMLVideoElement): (() => void) => {
+  const profile = createProfile();
+  window.__malHlsProfile = profile;
+
+  let stallStartedAt: number | null = null;
+  let seekStartedAt: number | null = null;
+
+  const onManifestLoading = (): void => {
+    profile.sourceLoads += 1;
+    mark("manifest_loading");
+  };
+
+  const onManifestParsed = (): void => {
+    profile.manifestParsed += 1;
+    measure("manifest_load", "manifest_loading");
+  };
+
+  const onHLSError = (_event: string, data: ErrorData): void => {
+    profile.errors += 1;
+    if (data.fatal) {
+      profile.fatalErrors += 1;
+    }
+    profile.lastErrorType = data.type;
+  };
+
+  const onWaiting = (): void => {
+    if (stallStartedAt !== null) return;
+    stallStartedAt = performance.now();
+    profile.stalls += 1;
+    mark("stall_start");
+  };
+
+  const onPlaying = (): void => {
+    if (stallStartedAt === null) return;
+    profile.totalStallMs += performance.now() - stallStartedAt;
+    stallStartedAt = null;
+    measure("stall", "stall_start");
+  };
+
+  const onSeeking = (): void => {
+    seekStartedAt = performance.now();
+    mark("seek_start");
+  };
+
+  const onSeeked = (): void => {
+    if (seekStartedAt === null) return;
+    profile.seeks += 1;
+    profile.totalSeekMs += performance.now() - seekStartedAt;
+    seekStartedAt = null;
+    measure("seek", "seek_start");
+  };
+
+  hls.on(Hls.Events.MANIFEST_LOADING, onManifestLoading);
+  hls.on(Hls.Events.MANIFEST_PARSED, onManifestParsed);
+  hls.on(Hls.Events.ERROR, onHLSError);
+  video.addEventListener("waiting", onWaiting);
+  video.addEventListener("playing", onPlaying);
+  video.addEventListener("seeking", onSeeking);
+  video.addEventListener("seeked", onSeeked);
+
+  return () => {
+    hls.off(Hls.Events.MANIFEST_LOADING, onManifestLoading);
+    hls.off(Hls.Events.MANIFEST_PARSED, onManifestParsed);
+    hls.off(Hls.Events.ERROR, onHLSError);
+    video.removeEventListener("waiting", onWaiting);
+    video.removeEventListener("playing", onPlaying);
+    video.removeEventListener("seeking", onSeeking);
+    video.removeEventListener("seeked", onSeeked);
+  };
+};
diff --git a/static/player/video.ts b/static/player/video.ts
index 6b0df55..741d98d 100644
--- a/static/player/video.ts
+++ b/static/player/video.ts
@@ -1,10 +1,14 @@
 import Hls from "hls.js";
+import { attachHLSProfile } from "./hls_profile";
 import { state } from "./state";
 import { absoluteTimeFromDisplay, displayTimeFromAbsolute, invalidateBounds } from "./timeline";
 
 let hls: Hls | null = null;
+let stopHLSProfile: (() => void) | null = null;
 
 const destroyHLS = (): void => {
+  stopHLSProfile?.();
+  stopHLSProfile = null;
   hls?.destroy();
   hls = null;
 };
@@ -44,6 +48,7 @@ export const loadVideoSource = (url: string, type?: string): void => {
 
   if (shouldUseHLS(type, url) && Hls.isSupported()) {
     hls = new Hls();
+    stopHLSProfile = attachHLSProfile(hls, state.video);
     hls.loadSource(url);
     hls.attachMedia(state.video);
   } else {