Cache preview frames for Discord video attachments

CURRENT.md

@@ -40,6 +40,10 @@ mobile draft at 390px.
   - [x] C11 preview caching: Discord-hosted image/GIF previews (WebP 320px, hash-addressed, 5 MiB
     cap, one attempt) run after every walk in both modes. Live run `...-20260916090722`:
     `previewed: 2`; thumbs served over `/api/media/<scrape>/<item>/thumb` (200).
+  - [x] C29 Attachment video previews. Discord's image proxy renders a frame for video files
+    (`?width=320&height=320&format=webp`), so `previewUrlFor` now resizes attachment mp4/webm in
+    links mode too and `pendingPreviews` includes non-embed videos. Live: paused-scrape videos
+    backfilled to `image/webp` thumbs, pending queue drained to 0.
   - [x] C28 Media grid usability. Infinite scroll (240 px threshold) with a Load more fallback,
     `previewError` exposed so tiles show PRIVATE (403) or GONE (404/410) with the reason in the
     tooltip, and the scrape strip lists only queued/running jobs — paused scrapes move to History.

docs/media-scraper.md

@@ -117,8 +117,11 @@ Downloads run after a finished walk when the scrape used `mode: "download"`:
 
 Previews run after every walk:
 
-- In both modes, Discord-hosted image and GIF URLs (`cdn.discordapp.com`, `media.discordapp.net`)
-  are transformed to the CDN resizer (`media.discordapp.net?...width=320&height=320&format=webp`).
+- In both modes, Discord-hosted image, GIF, and **video** URLs (`cdn.discordapp.com`,
+  `media.discordapp.net`) are transformed to the CDN resizer
+  (`media.discordapp.net?...width=320&height=320&format=webp`). The proxy renders a frame for
+  video files, so attachment mp4/webm get a cached poster in links mode without downloading the
+  file. Download mode additionally keeps an ffmpeg poster.
 - In both modes, embed rows also get their stored `preview_url` (YouTube, X, TikTok thumbnails,
   and so on) cached. The embed's full media URL is never fetched; embed rows are excluded from
   `pendingDownloads`.

docs/media.md

@@ -90,8 +90,9 @@ media-scrape/db/
   owns that path.
 - Third-party embeds are **never downloaded as media**: YouTube, Instagram, X, TikTok, and every
   other embed stays a link. Its thumbnail is cached (below); the video itself is never fetched.
-- Previews are cached in `thumbs/` after every walk, in both modes: Discord-hosted images and GIFs
-  (resized to 320px WebP) and third-party embed thumbnails (YouTube, X, TikTok, and so on). The
+- Previews are cached in `thumbs/` after every walk, in both modes: Discord-hosted images, GIFs,
+  and video files (the proxy renders a frame, resized to 320px WebP) plus third-party embed
+  thumbnails (YouTube, X, TikTok, and so on). The
   stored bytes keep their real type (`preview_ext`), so JPEG provider thumbnails are served as
   `image/jpeg`, not mislabeled WebP. Embeds without a thumbnail in Discord's data are resolved
   through the provider's oEmbed/fxtwitter API and finally the page's `og:image`. Previews count

media-scrape/src/download.ts

@@ -193,18 +193,17 @@ const DISCORD_HOSTS = new Set(["cdn.discordapp.com", "media.discordapp.net"]);
 /**
  * The preview target for a media row.
  *
- * Attachments and stickers: their Discord-hosted URL, resized to a small WebP.
+ * Attachments and stickers: their Discord-hosted URL, resized to a small WebP. Discord's proxy
+ * also renders a frame for video files, so attachment videos get a poster for free.
  * Embeds: the stored thumbnail or image URL, used as-is (Discord-hosted ones are still resized).
- * Returns null when the row has no preview source.
+ * A bare embed URL is a page, never a preview. Returns null when the row has no preview source.
  */
 export function previewUrlFor(media: {
     url: string;
     kind: string;
     previewUrl?: string | null;
 }): string | null {
-    const candidate =
-        media.previewUrl ??
-        (media.kind === "image" || media.kind === "gif" ? media.url : null);
+    const candidate = media.previewUrl ?? media.url;
     if (!candidate) return null;
 
     try {
@@ -214,8 +213,13 @@ export function previewUrlFor(media: {
             url.searchParams.set("width", "320");
             url.searchParams.set("height", "320");
             url.searchParams.set("format", "webp");
+            return url.toString();
         }
-        return url.toString();
+
+        if (media.previewUrl || media.kind === "image" || media.kind === "gif") {
+            return url.toString();
+        }
+        return null;
     } catch {
         return null;
     }

media-scrape/src/store.ts

@@ -342,7 +342,8 @@ export class ScrapeStore {
      * embed thumbnails only when `includeEmbeds` is set (download mode).
      */
     pendingPreviews(limit = 5000, includeEmbeds = false): MediaRow[] {
-        const local = "(kind IN ('image', 'gif') AND (source IS NULL OR source != 'embed'))";
+        const local =
+            "((source IS NULL OR source != 'embed') AND kind IN ('image', 'gif', 'video'))";
         const condition = includeEmbeds
             ? `(${local} OR (source = 'embed' AND preview_url IS NOT NULL))`
             : local;

media-scrape/test/run.ts

@@ -522,6 +522,10 @@ void (async () => {
             "https://media.discordapp.net/attachments/1/2/pic.png?width=320&height=320&format=webp"
         );
         assert.equal(previewUrlFor({ url: "https://www.youtube.com/watch?v=x", kind: "video" }), null);
+        assert.equal(
+            previewUrlFor({ url: "https://cdn.discordapp.com/attachments/1/2/clip.mp4?ex=abc", kind: "video" }),
+            "https://media.discordapp.net/attachments/1/2/clip.mp4?ex=abc&width=320&height=320&format=webp"
+        );
         assert.equal(
             previewUrlFor({
                 url: "https://www.youtube.com/watch?v=x",
@@ -599,7 +603,10 @@ void (async () => {
             {
                 messages: [
                     message("600", {
-                        attachments: [attachment({ filename: "prev.png", contentType: "image/png" })],
+                        attachments: [
+                            attachment({ filename: "prev.png", contentType: "image/png" }),
+                            attachment({ filename: "clip.mp4", contentType: "video/mp4" })
+                        ],
                         embeds: [
                             {
                                 type: "video",
@@ -643,9 +650,10 @@ void (async () => {
 
         const meta = engine.get(started.id);
         assert.equal(meta?.state, "done");
-        assert.equal(meta?.previewed, 2);
+        assert.equal(meta?.previewed, 3);
         assert.equal(fetched.some(url => url.includes("ytimg.com")), true);
         assert.equal(fetched.some(url => url.includes("youtube.com/watch")), false);
+        assert.equal(fetched.some(url => url.includes("clip.mp4") && url.includes("format=webp")), true);
 
         const store = new ScrapeStore(join(root, started.id));
         const row = store.queryMedia({ kind: "image" })[0];