feat(timeline): muted hover-to-play preview on video tiles

PhotoPrism plays a silent preview of the actual video when you hover
its grid tile; this mirrors that. After a 250ms debounce the tile
mounts a muted, looping <video> over the thumbnail and cross-fades it
in on first decoded frame, so cursor-skimming doesn't fire N requests
and the tile never blanks mid-fetch. The byte-prefetch helper added
in af96922 is now redundant — the hover <video> warms the same caches
on its own.

Also tells Vidstack the playback URL is video/mp4 via a nested
<source>: our /api/v1/videos/.../avc URL has no extension, so
Vidstack's suffix sniff was failing, falling back to a HEAD probe,
and picking the wrong loader (which surfaced as
NS_ERROR_DOM_MEDIA_METADATA_ERR in Firefox).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/lib/components/preview/VideoPlayer.svelte

@@ -34,23 +34,29 @@
 </script>
 
 {#if ready}
-	<!-- svelte-ignore element_invalid_self_closing_tag -->
+	<!--
+		Note: `src` is *not* set as an attribute on <media-player>. Our backend
+		URL ends in `/avc` (not `.mp4`), so Vidstack's URL-suffix sniff fails
+		and it falls back to a HEAD probe — which can pick the wrong loader
+		and produce decode errors. Declaring the source via a nested
+		<source type="video/mp4"> tells Vidstack to use the native MP4 loader
+		directly, no probe needed.
+	-->
 	<media-player
 		class="vds-player max-h-full max-w-full rounded-md shadow-2xl"
 		title={title ?? ''}
-		{src}
 		{poster}
 		autoplay
 		muted
 		playsinline
 		load="eager"
 		posterLoad="eager"
-		crossorigin=""
-		preferNativeHLS="false"
 		streamType="on-demand"
 		viewType="video"
 	>
-		<media-provider></media-provider>
+		<media-provider>
+			<source {src} type="video/mp4" />
+		</media-provider>
 		<media-video-layout></media-video-layout>
 	</media-player>
 {:else}

web/src/lib/components/timeline/PhotoTile.svelte

@@ -16,9 +16,8 @@
 -->
 <script lang="ts">
 	import { Maximize2 } from 'lucide-svelte';
-	import { thumbSrc, thumbSrcSet } from '$lib/stores/session.svelte';
+	import { thumbSrc, thumbSrcSet, videoUrl } from '$lib/stores/session.svelte';
 	import { view } from '$lib/stores/view.svelte';
-	import { cancelVideoPrefetch, startVideoPrefetch } from '$lib/stores/videoPrefetch.svelte';
 	import { isVideo, primaryFile, type PpPhoto } from '$lib/types/photoprism';
 
 	interface Props {
@@ -33,14 +32,30 @@
 	const hash = $derived(photo.Hash ?? primaryFile(photo).Hash);
 	const video = $derived(isVideo(photo));
 
-	// Warm the video transcode + browser HTTP cache on hover so opening the
-	// preview feels instant. The helper de-bounces internally — we just
-	// fire-and-cancel on the hover edges.
+	// Hover preview: PhotoPrism plays a muted, looping preview of the actual
+	// video when you hover the tile in the grid. We wait HOVER_DELAY ms
+	// before mounting the <video> so a cursor skimming across the grid
+	// doesn't kick off N HTTP requests, then we cross-fade in once the
+	// first frame is decoded (videoReady).
+	const HOVER_DELAY = 250;
+	let hoverPlaying = $state(false);
+	let videoReady = $state(false);
+	let hoverTimer: ReturnType<typeof setTimeout> | null = null;
+
 	function onMouseEnter() {
-		if (video) startVideoPrefetch(hash);
+		if (!video || selected) return;
+		if (hoverTimer) clearTimeout(hoverTimer);
+		hoverTimer = setTimeout(() => {
+			hoverPlaying = true;
+		}, HOVER_DELAY);
 	}
 	function onMouseLeave() {
-		if (video) cancelVideoPrefetch(hash);
+		if (hoverTimer) {
+			clearTimeout(hoverTimer);
+			hoverTimer = null;
+		}
+		hoverPlaying = false;
+		videoReady = false;
 	}
 	// Render-size hint for the browser's srcset picker. `view.thumbnailSize`
 	// is the grid's `minmax(<px>, 1fr)` minimum — real tiles may be a hair
@@ -103,6 +118,29 @@
 			class:transition={!selected}
 			class:group-hover:scale-105={!selected}
 		/>
+		{#if hoverPlaying}
+			<!--
+				Muted hover-preview video stacked over the thumbnail. We don't
+				unmount the <img> underneath — the video fades in once its
+				first frame is decoded, so the tile never goes blank during
+				the network round-trip. `pointer-events-none` keeps clicks
+				flowing through to the parent <button>.
+			-->
+			<!-- svelte-ignore a11y_media_has_caption -->
+			<video
+				src={videoUrl(hash)}
+				autoplay
+				muted
+				loop
+				playsinline
+				preload="auto"
+				tabindex={-1}
+				oncanplay={() => (videoReady = true)}
+				class="pointer-events-none absolute inset-0 h-full w-full object-cover transition-opacity duration-200"
+				class:opacity-0={!videoReady}
+				class:opacity-100={videoReady}
+			></video>
+		{/if}
 		{#if selected}
 			<div class="pointer-events-none absolute inset-0 bg-blue-500/40"></div>
 		{/if}

web/src/lib/stores/videoPrefetch.svelte.ts

@@ -1,60 +0,0 @@
-/**
- * Hover-warm cache for video playback URLs.
- *
- * When a user hovers a video tile, we ask the browser to fetch the first
- * chunk of the playback URL. That single Range request:
- *   1. Forces the backend's pre-transcoded MP4 cache file open (paging it
- *      into the OS page cache so the real player request hits warm bytes).
- *   2. Lands in the browser's HTTP cache, so when the player mounts and
- *      issues its own Range: bytes=0- request the response is satisfied
- *      from disk and playback starts within a frame or two.
- *
- * We delay the fetch slightly so users who are scrubbing their cursor
- * across the grid don't pay the cost; cancellation via AbortController
- * keeps wasted bytes bounded.
- *
- * Each hash is warmed at most once per session — the prefetch is purely
- * cache-warming, so a second hover would be a no-op anyway.
- */
-import { videoUrl } from '$lib/stores/session.svelte';
-
-const HOVER_DELAY_MS = 120;
-const PREFETCH_BYTES = 524288; // 512 KB — enough to start playback in most cases.
-
-const warmed = new Set<string>();
-const pending = new Map<string, { timer: number; controller: AbortController }>();
-
-export function startVideoPrefetch(hash: string): void {
-	if (!hash || warmed.has(hash) || pending.has(hash)) return;
-
-	const url = videoUrl(hash);
-	if (!url) return;
-
-	const controller = new AbortController();
-	const timer = window.setTimeout(async () => {
-		try {
-			await fetch(url, {
-				method: 'GET',
-				headers: { Range: `bytes=0-${PREFETCH_BYTES - 1}` },
-				signal: controller.signal,
-				credentials: 'same-origin',
-				cache: 'default'
-			});
-			warmed.add(hash);
-		} catch {
-			// Aborted hovers or network blips are expected — silently drop.
-		} finally {
-			pending.delete(hash);
-		}
-	}, HOVER_DELAY_MS);
-
-	pending.set(hash, { timer, controller });
-}
-
-export function cancelVideoPrefetch(hash: string): void {
-	const entry = pending.get(hash);
-	if (!entry) return;
-	clearTimeout(entry.timer);
-	entry.controller.abort();
-	pending.delete(hash);
-}