src/components/MobileFeed.tsx

@@ -10,6 +10,7 @@ import { CaptionText, QuoteText } from "./SlideText";
 import { FeaturedCarousel } from "./FeaturedCarousel";
 import { Logo } from "./Logo";
 import { useTheme } from "@/lib/use-theme";
+import { getSessionMuted, isAutoplayBlocked, setSessionMuted } from "@/lib/autoplay";
 import { MobileDock } from "./MobileDock";
 import { BottomSheet } from "./BottomSheet";
 import { CommentsSection } from "./CommentsSection";
@@ -86,33 +87,137 @@ export function videoFit(width: number, height: number): "cover" | "contain" {
   return width / height <= COVER_MAX_RATIO ? "cover" : "contain";
 }
 
-function SlideMedia({ media, author }: { media: CardMedia; author: string }) {
+/** True when the person asked for less motion. Updates when the setting changes; false on the server. */
+function useReducedMotion(): boolean | null {
+  const [reduced, setReduced] = useState<boolean | null>(null);
+  useEffect(() => {
+    if (typeof window.matchMedia !== "function") return setReduced(false);
+    const mq = window.matchMedia("(prefers-reduced-motion: reduce)");
+    const read = () => setReduced(mq.matches);
+    read();
+    mq.addEventListener?.("change", read);
+    return () => mq.removeEventListener?.("change", read);
+  }, []);
+  return reduced;
+}
+
+function SoundIcon({ muted }: { muted: boolean }) {
+  return (
+    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="1.8" strokeLinecap="round" strokeLinejoin="round" aria-hidden="true">
+      <path d="M11 5 6 9H3v6h3l5 4V5z" />
+      {muted ? <path d="m16 9 5 6M21 9l-5 6" /> : <path d="M15.5 8.5a5 5 0 0 1 0 7M18.5 5.5a9 9 0 0 1 0 13" />}
+    </svg>
+  );
+}
+
+/**
+ * One media item of a slide. A video plays by itself, muted and inline, while
+ * `active` (its slide and pane are on screen) unless the person asked for less
+ * motion or the browser refuses: then the play button starts it as before.
+ * `hold` (a sheet is open) pauses a playing video and resumes it after.
+ */
+function SlideMedia({ media, author, active = false, hold = false }: { media: CardMedia; author: string; active?: boolean; hold?: boolean }) {
   const box = useRef<HTMLDivElement>(null);
   const [started, setStarted] = useState(false);
   // Real video size once metadata loads; until then the thumbnail's size decides.
   const [videoSize, setVideoSize] = useState<[number, number] | null>(null);
   const [thumbSize, setThumbSize] = useState<[number, number] | null>(null);
   const playable = isPlayableVideo(media);
+  const reduced = useReducedMotion();
+  // The browser refused autoplay: fall back to the play button.
+  const [blocked, setBlocked] = useState(false);
+  const auto = reduced === false && !blocked;
+  const [muted, setMuted] = useState(getSessionMuted);
+  // Paused by a tap: it stays paused until tapped again or the slide leaves.
+  const [userPaused, setUserPaused] = useState(false);
+  const userPausedRef = useRef(false);
+  const resumeAfterHold = useRef(false);
+  const video = () => box.current?.querySelector("video") ?? null;
   useEffect(() => {
-    const video = box.current?.querySelector("video");
+    const v = video();
-    if (!video) return;
+    if (!v) return;
     const read = () => {
-      if (video.videoWidth > 0 && video.videoHeight > 0) setVideoSize([video.videoWidth, video.videoHeight]);
+      if (v.videoWidth > 0 && v.videoHeight > 0) setVideoSize([v.videoWidth, v.videoHeight]);
     };
     read();
-    video.addEventListener("loadedmetadata", read);
+    v.addEventListener("loadedmetadata", read);
-    return () => video.removeEventListener("loadedmetadata", read);
+    return () => v.removeEventListener("loadedmetadata", read);
   }, [playable, media.mp4Url, media.hlsUrl]);
+
+  const autoplay = useCallback((v: HTMLVideoElement) => {
+    v.muted = getSessionMuted();
+    // Like a reel, an autoplayed video loops while it is on screen.
+    v.loop = true;
+    setMuted(v.muted);
+    v.play().catch((err: unknown) => {
+      if (!isAutoplayBlocked(err)) return;
+      // Sound not allowed yet: play muted this time, keeping the session's choice.
+      if (!v.muted) {
+        v.muted = true;
+        setMuted(true);
+        v.play().catch((again: unknown) => {
+          if (isAutoplayBlocked(again)) setBlocked(true);
+        });
+      } else setBlocked(true);
+    });
+  }, []);
+
+  useEffect(() => {
+    const v = video();
+    if (!v || !playable) return;
+    if (!active) {
+      userPausedRef.current = false;
+      setUserPaused(false);
+      resumeAfterHold.current = false;
+      v.pause();
+      return;
+    }
+    if (hold) {
+      if (!v.paused) {
+        resumeAfterHold.current = true;
+        v.pause();
+      }
+      return;
+    }
+    if (resumeAfterHold.current) {
+      resumeAfterHold.current = false;
+      void v.play().catch(() => {});
+      return;
+    }
+    if (auto && !userPausedRef.current) autoplay(v);
+  }, [active, hold, auto, playable, autoplay]);
+
   if (playable) {
     const size = videoSize ?? thumbSize;
     const fit = size ? videoFit(size[0], size[1]) : "cover";
     const duration = formatDuration(media.durationSeconds);
     const start = () => {
       setStarted(true);
-      void box.current?.querySelector("video")?.play().catch(() => {});
+      const v = video();
+      if (!v) return;
+      v.muted = false;
+      void v.play().catch(() => {});
     };
+    // Autoplay: a tap on the video pauses or resumes it (no native controls).
+    const togglePause = () => {
+      const v = video();
+      if (!v) return;
+      const pause = !v.paused;
+      userPausedRef.current = pause;
+      setUserPaused(pause);
+      if (pause) v.pause();
+      else void v.play().catch(() => {});
+    };
+    const toggleMute = () => {
+      const v = video();
+      const next = !muted;
+      if (v) v.muted = next;
+      setSessionMuted(next);
+      setMuted(next);
+    };
+    const showPlay = auto ? userPaused : !started;
     return (
-      <div className="slide-media slide-video" data-fit={fit} ref={box}>
+      <div className="slide-media slide-video" data-fit={fit} data-autoplay={auto ? "true" : undefined} ref={box}>
         {media.src ? (
           // The thumbnail doubles as the blurred backdrop behind a contained video, and as the size fallback.
           // eslint-disable-next-line @next/next/no-img-element
@@ -124,17 +229,36 @@ function SlideMedia({ media, author }: { media: CardMedia; author: string }) {
             onLoad={(e) => setThumbSize([e.currentTarget.naturalWidth, e.currentTarget.naturalHeight])}
           />
         ) : null}
-        <div className="slide-art">
+        <div className="slide-art" onClick={auto ? togglePause : undefined}>
-          <VideoPlayer mp4Url={media.mp4Url} hlsUrl={media.hlsUrl} poster={media.src} label={`Video from ${author}`} controls={started} />
+          <VideoPlayer
+            mp4Url={media.mp4Url}
+            hlsUrl={media.hlsUrl}
+            poster={media.src}
+            label={`Video from ${author}`}
+            controls={!auto && started}
+            muted={auto ? muted : undefined}
+          />
         </div>
-        {started ? null : (
+        {auto ? (
+          <button
+            type="button"
+            className="slide-mute"
+            data-testid="slide-mute"
+            aria-label={muted ? "Unmute video" : "Mute video"}
+            aria-pressed={!muted}
+            onClick={toggleMute}
+          >
+            <SoundIcon muted={muted} />
+          </button>
+        ) : null}
+        {showPlay ? (
           <>
-            <button type="button" className="post-play slide-play" aria-label="Play video" onClick={start}>
+            <button type="button" className="post-play slide-play" aria-label="Play video" onClick={auto ? togglePause : start}>
               <PlayIcon />
             </button>
-            {duration ? <span className="post-dur slide-dur">{duration}</span> : null}
+            {duration && !auto ? <span className="post-dur slide-dur">{duration}</span> : null}
           </>
-        )}
+        ) : null}
       </div>
     );
   }
@@ -154,7 +278,7 @@ function SlideMedia({ media, author }: { media: CardMedia; author: string }) {
 }
 
 /** Several media items in one slide: a sideways scroll-snap track with a dot per item. */
-function MediaTrack({ items, author }: { items: CardMedia[]; author: string }) {
+function MediaTrack({ items, author, current, hold }: { items: CardMedia[]; author: string; current: boolean; hold: boolean }) {
   const track = useRef<HTMLDivElement>(null);
   const [active, setActive] = useState(0);
   const onScroll = () => {
@@ -173,7 +297,7 @@ function MediaTrack({ items, author }: { items: CardMedia[]; author: string }) {
       <div className="slide-track" data-testid="slide-track" ref={track} onScroll={onScroll}>
         {items.map((m, i) => (
           <div className="slide-pane" key={i} aria-label={`Media ${i + 1} of ${items.length}`}>
-            <SlideMedia media={m} author={author} />
+            <SlideMedia media={m} author={author} active={current && i === active} hold={hold} />
           </div>
         ))}
       </div>
@@ -190,19 +314,22 @@ function PostSlide({
   post,
   index,
   current,
+  hold,
   p,
   onExpandedChange,
 }: {
   post: CardPost;
   index: number;
   current: boolean;
+  /** A sheet is open over the feed: a playing video pauses until it closes. */
+  hold: boolean;
   p: FeedViewProps;
   onExpandedChange?: (index: number, open: boolean) => void;
 }) {
   const items = post.media.filter((m) => m.kind === "video" || m.src);
   const media = items[0] ?? null;
   const own = canDelete(post, p.feedUserId) && !!p.onDelete;
-  // While a video plays, the author and text step aside so the native controls stay clear.
+  // While a video plays with native controls (play button, not autoplay), the author and text step aside.
   const [playing, setPlaying] = useState(false);
   // Long text opened with "Read more" or "more". It closes when the slide leaves the screen.
   const [textOpen, setTextOpen] = useState(false);
@@ -240,13 +367,19 @@ function PostSlide({
       data-liked={post.isLiked ? "true" : "false"}
       onClick={onTap}
       aria-label={`Post by ${post.authorName}`}
-      onPlayCapture={() => setPlaying(true)}
+      onPlayCapture={(e) => {
+        if ((e.target as HTMLVideoElement).controls) setPlaying(true);
+      }}
       onPauseCapture={() => setPlaying(false)}
       onEndedCapture={() => setPlaying(false)}
     >
       {media ? (
         <>
-          {items.length > 1 ? <MediaTrack items={items} author={post.authorName} /> : <SlideMedia media={media} author={post.authorName} />}
+          {items.length > 1 ? (
+            <MediaTrack items={items} author={post.authorName} current={current} hold={hold} />
+          ) : (
+            <SlideMedia media={media} author={post.authorName} active={current} hold={hold} />
+          )}
           <div className="slide-scrim-top" aria-hidden="true" />
           <div className="slide-scrim" aria-hidden="true" />
         </>
@@ -515,7 +648,7 @@ export function MobileFeed(p: FeedViewProps) {
         ) : null}
         {p.status === "ready"
           ? p.posts.flatMap((post, i) => {
-              const node = <PostSlide key={post.key} post={post} index={slideOf(i)} current={slideOf(i) === index} p={p} onExpandedChange={onExpandedChange} />;
+              const node = <PostSlide key={post.key} post={post} index={slideOf(i)} current={slideOf(i) === index} hold={sheet !== null} p={p} onExpandedChange={onExpandedChange} />;
               return i === featuredAt - 1
                 ? [node, <FeaturedSlide key="featured" index={featuredAt} current={index === featuredAt} experts={experts} />]
                 : [node];

src/components/VideoPlayer.tsx

@@ -10,6 +10,8 @@ export interface VideoPlayerProps {
   label: string;
   /** Native controls; off until the caller's own play button starts the video. Default on. */
   controls?: boolean;
+  /** Start muted (the mobile feed's autoplay). Desktop leaves it unset. */
+  muted?: boolean;
 }
 
 const UNPLAYABLE = "Video can't be played here.";
@@ -18,9 +20,9 @@ const UNPLAYABLE = "Video can't be played here.";
  * Real <video controls>. Order: direct mp4Url (plain progressive source), else
  * hls.js (lazy-loaded, only for the HLS path; native HLS only where hls.js is
  * unsupported), else thumbnail only. Never
- * autoplays. Any failure falls back to the thumbnail with a short note.
+ * autoplays by itself (the mobile feed starts it). Any failure falls back to the thumbnail with a short note.
  */
-export function VideoPlayer({ mp4Url, hlsUrl, poster, label, controls = true }: VideoPlayerProps) {
+export function VideoPlayer({ mp4Url, hlsUrl, poster, label, controls = true, muted }: VideoPlayerProps) {
   const ref = useRef<HTMLVideoElement>(null);
   const [failed, setFailed] = useState(false);
 
@@ -80,6 +82,7 @@ export function VideoPlayer({ mp4Url, hlsUrl, poster, label, controls = true }:
       ref={ref}
       src={mp4Url ?? undefined}
       controls={controls}
+      muted={muted}
       playsInline
       preload="none"
       poster={poster ?? undefined}

src/lib/autoplay.ts

@@ -0,0 +1,24 @@
+/**
+ * Mobile feed autoplay: the session's mute choice and how a failed play() is read.
+ * The choice lives in memory only, for this page session: videos start muted
+ * (browsers only autoplay muted video) until the person unmutes one.
+ */
+let sessionMuted = true;
+
+/** True until the person unmutes a video in this session. */
+export function getSessionMuted(): boolean {
+  return sessionMuted;
+}
+
+/** Remember the person's mute choice for the videos that play after this one. */
+export function setSessionMuted(muted: boolean): void {
+  sessionMuted = muted;
+}
+
+/**
+ * True when play() was refused by the browser's autoplay policy. A play() that
+ * was cut short by pause() (AbortError) is not a refusal.
+ */
+export function isAutoplayBlocked(error: unknown): boolean {
+  return !!error && typeof error === "object" && (error as { name?: unknown }).name === "NotAllowedError";
+}

src/styles/mobile.css

@@ -73,6 +73,32 @@
 .slide-pending { display: grid; place-items: center; color: var(--ink-2); font-size: 14px; }
 .slide-play { z-index: 4; }
 .slide-dur { top: 128px; right: 16px; z-index: 4; }
+/* Autoplay: a small frosted sound toggle on the video; a tap on the video pauses or resumes it. */
+.slide-video[data-autoplay="true"] .slide-art { cursor: pointer; }
+.slide-mute {
+  position: absolute;
+  top: calc(72px + env(safe-area-inset-top, 0px));
+  right: 16px;
+  z-index: 4;
+  display: grid;
+  place-items: center;
+  width: 36px;
+  height: 36px;
+  margin: 0;
+  padding: 0;
+  border: 0;
+  border-radius: 12px;
+  appearance: none;
+  color: var(--on-media);
+  background: var(--media-glass);
+  -webkit-backdrop-filter: blur(16px) saturate(1.6);
+  backdrop-filter: blur(16px) saturate(1.6);
+  box-shadow: inset 0 0 0 1px var(--on-media-line);
+  cursor: pointer;
+  transition: transform .2s var(--ease);
+}
+.slide-mute svg { width: 18px; height: 18px; }
+.slide-mute:active { transform: scale(.92); }
 
 /* Several media items: a sideways snap track; each pane is one full-slide item. */
 .slide-track {

tests/autoplay.test.ts

@@ -0,0 +1,46 @@
+import { describe, expect, it } from "vitest";
+import { createElement } from "react";
+import { renderToStaticMarkup } from "react-dom/server";
+import { readFileSync } from "node:fs";
+import { getSessionMuted, isAutoplayBlocked, setSessionMuted } from "@/lib/autoplay";
+import { VideoPlayer } from "@/components/VideoPlayer";
+
+describe("session mute choice", () => {
+  it("starts muted and keeps the person's choice", () => {
+    expect(getSessionMuted()).toBe(true);
+    setSessionMuted(false);
+    expect(getSessionMuted()).toBe(false);
+    setSessionMuted(true);
+    expect(getSessionMuted()).toBe(true);
+  });
+});
+
+describe("autoplay refusal", () => {
+  it("only counts the browser's NotAllowedError", () => {
+    expect(isAutoplayBlocked({ name: "NotAllowedError" })).toBe(true);
+    expect(isAutoplayBlocked({ name: "AbortError" })).toBe(false);
+    expect(isAutoplayBlocked(null)).toBe(false);
+    expect(isAutoplayBlocked("NotAllowedError")).toBe(false);
+  });
+});
+
+describe("VideoPlayer", () => {
+  it("is inline and not muted unless asked (desktop unchanged)", () => {
+    const html = renderToStaticMarkup(createElement(VideoPlayer, { mp4Url: "https://cdn/v.mp4", poster: null, label: "v" }));
+    expect(html).toContain("playsInline");
+    expect(html).toContain("controls");
+    expect(html).not.toContain("muted");
+  });
+  it("renders muted inline video for the mobile autoplay", () => {
+    const html = renderToStaticMarkup(createElement(VideoPlayer, { mp4Url: "https://cdn/v.mp4", poster: null, label: "v", controls: false, muted: true }));
+    expect(html).toContain("muted");
+    expect(html).not.toContain("controls");
+  });
+});
+
+describe("mobile autoplay styles", () => {
+  it("has a frosted mute button", () => {
+    const css = readFileSync("src/styles/mobile.css", "utf8");
+    expect(css).toMatch(/\.slide-mute \{[^}]*backdrop-filter/);
+  });
+});