Video stills: past a black opening. vmedia took its still at half a second, and a clip that fades in from black (7 of the 68 made in three hours) gave a black tile. Each frame's mean brightness now comes out of ffmpeg (signalstats YAVG on pipe:2 — /dev/stderr can't be opened from a Bun-spawned pipe), and a dark one sends it further in (2, 5, 10, 20, 40 s) for the first bright frame; a clip dark all the way through (a night scene, a boot screen) gets its brightest frame with the levels stretched (normalize). Stills are made again under a new key and URL (v=4), so neither the server's nor the CDN's black copies are served.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Vps2H27rhbG9ZqseGfMrc3

3 files changed, 32 insertions, 9 deletions

diff --git a/src/features/messages.js b/src/features/messages.js
index ed4136a..6245c60 100644
--- a/src/features/messages.js
+++ b/src/features/messages.js
@@ -7178,7 +7178,8 @@ export function messagesFeature(ctx) {
   // for Linux plays its sound over black.
   const VMEDIA = APP_BASE + '/vmedia/';
   const vmediaOk = (url) => /^https:\/\//i.test(url || '');
-  const serverThumb = (url) => (vmediaOk(url) ? VMEDIA + 'thumb.jpg?u=' + encodeURIComponent(url) : undefined);
+  // v=4: stills past a dark opening frame (a new URL, so the CDN's old black ones aren't served)
+  const serverThumb = (url) => (vmediaOk(url) ? VMEDIA + 'thumb.jpg?v=4&u=' + encodeURIComponent(url) : undefined);
   const h264Of = (url) => VMEDIA + 'h264.mp4?u=' + encodeURIComponent(url);
   const noPicture = new Set(), h264Failed = new Set();
   const serverThumbFailed = new Set(); // clips vmedia had no picture for (this session)
diff --git a/tools/video-fallback-test.js b/tools/video-fallback-test.js
index 66becc2..85250c0 100644
--- a/tools/video-fallback-test.js
+++ b/tools/video-fallback-test.js
@@ -93,7 +93,7 @@ try {
 
   console.log('\n[no poster in the post]');
   const p0 = await player('garden');
-  check('the server\'s still is the poster', p0.poster === 'https://v3.coinos.io/vmedia/thumb.jpg?u=' + encodeURIComponent(CLIP.saved), p0.poster);
+  check('the server\'s still is the poster', p0.poster === 'https://v3.coinos.io/vmedia/thumb.jpg?v=4&u=' + encodeURIComponent(CLIP.saved), p0.poster);
 
   console.log('\n[waiting for a tap]');
   await page.evaluate(new Function(`${box('garden')}.scrollIntoView({ block: 'center' })`));
diff --git a/vmedia/server.js b/vmedia/server.js
index bf92c6b..c543d6c 100644
--- a/vmedia/server.js
+++ b/vmedia/server.js
@@ -59,8 +59,11 @@ export async function sourceOk(raw, resolve = (h) => lookup(h, { all: true })) {
 const NET = ['-protocol_whitelist', 'https,tls,tcp,crypto', '-rw_timeout', '15000000', '-user_agent', 'coinos-vmedia'];
 // longest side at most 1280, even numbers for the encoder
 export const SCALE_720 = "scale='trunc(min(1,1280/max(iw,ih))*iw/2)*2':'trunc(min(1,1280/max(iw,ih))*ih/2)*2'";
-export const thumbArgs = (src, at) => ['-hide_banner', '-loglevel', 'error', ...NET, ...(at ? ['-ss', String(at)] : []), '-i', src,
-  '-frames:v', '1', '-vf', "scale='min(480,iw)':-2", '-q:v', '5', '-f', 'image2', '-c:v', 'mjpeg', 'pipe:1'];
+export const thumbArgs = (src, at, lift = false) => ['-hide_banner', '-loglevel', 'error', ...NET, ...(at ? ['-ss', String(at)] : []), '-i', src,
+  // the frame's mean brightness rides out on stderr (YAVG, 0–255): a clip
+  // that fades in from black has a black frame at half a second
+  '-frames:v', '1', '-vf', "scale='min(480,iw)':-2," + (lift ? 'normalize=strength=0.7:smoothing=0,' : '') + "signalstats,metadata=mode=print:key=lavfi.signalstats.YAVG:file='pipe\\:2'",
+  '-q:v', '5', '-f', 'image2', '-c:v', 'mjpeg', 'pipe:1'];
 export const clipArgs = (src, out) => ['-hide_banner', '-loglevel', 'error', '-y', ...NET, '-i', src,
   '-map', '0:v:0', '-map', '0:a:0?', '-t', String(MAX_SECONDS), '-vf', SCALE_720,
   '-c:v', 'libx264', '-preset', 'veryfast', '-crf', '26', '-profile:v', 'high', '-pix_fmt', 'yuv420p', '-threads', '4',
@@ -90,18 +93,37 @@ function limiter(n) {
 // ---- thumbnails -----------------------------------------------------------
 const thumbSlots = limiter(THUMB_JOBS);
 const thumbJobs = new Map();
+// Half a second in, unless that frame is (nearly) black — an intro fading
+// in, a title card on black — then further in, keeping the first frame bright
+// enough to show what the clip is. A clip shorter than a given point simply
+// yields nothing there. A clip dark all the way through (a night scene) gets
+// its brightest frame with the levels stretched, so the tile shows what's in
+// it rather than a black square. YAVG is limited-range: black is 16.
+const DARK = 28;
 async function makeThumb(src, key) {
   const out = `${THUMBS}/${key}.jpg`;
-  for (const at of [0.5, 0]) { // a clip shorter than half a second has only its start
-    const { p, done } = run(thumbArgs(src, at), 25_000);
-    const [buf] = await Promise.all([new Response(p.stdout).arrayBuffer(), done]);
-    if (p.exitCode === 0 && buf.byteLength > 500) { await Bun.write(out, buf); return out; }
+  let best = null;
+  const grab = async (at, lift) => {
+    const { p, done } = run(thumbArgs(src, at, lift), 25_000);
+    const [buf, err] = await Promise.all([new Response(p.stdout).arrayBuffer(), new Response(p.stderr).text(), done]);
+    if (p.exitCode !== 0 || buf.byteLength <= 500) return null;
+    return { buf, at, y: Number((/YAVG=([\d.]+)/.exec(err) || [])[1] ?? 255) };
+  };
+  for (const at of [0.5, 2, 5, 10, 20, 40, 0]) {
+    if (at === 0 && best) break; // the very start only when nothing later worked
+    const got = await grab(at, false);
+    if (!got) continue;
+    if (!best || got.y > best.y) best = got;
+    if (got.y >= DARK) break;
   }
+  if (best && best.y < DARK) best = (await grab(best.at, true)) || best;
+  if (best) { await Bun.write(out, best.buf); return out; }
   failed.set(key, Date.now());
   return null;
 }
+const THUMB_V = 4; // v4: past a dark opening frame (stills made before are made again)
 async function thumb(src) {
-  const key = keyOf(src), out = `${THUMBS}/${key}.jpg`;
+  const key = keyOf('v' + THUMB_V + '|' + src), out = `${THUMBS}/${key}.jpg`;
   if (existsSync(out)) { touch(out); return out; }
   if (failedLately(key)) return null;
   if (!thumbJobs.has(key)) thumbJobs.set(key, thumbSlots(() => makeThumb(src, key)).finally(() => thumbJobs.delete(key)));