diff --git a/CURRENT.md b/CURRENT.md
index b2b9d9b..c6e6d9a 100644
--- a/CURRENT.md
+++ b/CURRENT.md
@@ -40,6 +40,12 @@ 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] C27 Non-media stream guard. Rows awaiting backfill fell back to first-frame `<video>` with
+    a provider page URL (YouTube embed, redirectors), and the stream route piped the HTML through
+    (`text/html` errors). Now only real video files (mp4/webm/m4v) are framed, the stream route
+    returns `415` for non-media upstreams, the viewer's still-frame is gated the same way, and
+    "Open in new tab" prefers `play_url`. Live: YouTube item → 415 JSON; backfill reached
+    184/271 previews during the run.
   - [x] C26 YouTube preview root cause. Dedupe picked the newest row per URL; a paused scrape
     (`gernal_chut`, stopped mid-walk) had no previews yet and hid an older scrape that did. Fixes:
     dedupe prefers the richer row (downloaded > preview > newer), paused walks still run the
diff --git a/docs/media.md b/docs/media.md
index 19bd10d..7eba850 100644
--- a/docs/media.md
+++ b/docs/media.md
@@ -158,7 +158,9 @@ that deletion is irreversible. The delete button is disabled for a 5 second coun
   `  /api/media/<scrape>/<item>/stream`, which serves the local file or re-fetches the source message
   for a fresh signed URL, so expired CDN links still play. The grid prefers the cached still; a
   video without one gets its first frame through the same-origin stream endpoint, which avoids
-  cross-origin blocking and URL expiry. Embed `videoUrl`s (gifv/Tenor mp4s) are stored as
+  cross-origin blocking and URL expiry. Only real video-file URLs are framed; provider pages
+  (YouTube embeds, redirector URLs) are never, and the stream route answers `415` when the
+  upstream is not media — so a pending preview shows a placeholder instead of a browser error. Embed `videoUrl`s (gifv/Tenor mp4s) are stored as
   `play_url` and used through the stream. The full link is a separate button that opens the
   original page with the warning. Length comes from Discord's attachment duration and, for
   downloads, an ffprobe probe. GIF tiles carry a translucent **GIF** label top-left; the cached
diff --git a/docs/webui.md b/docs/webui.md
index 40c9378..aaeb081 100644
--- a/docs/webui.md
+++ b/docs/webui.md
@@ -261,7 +261,7 @@ replaceable.
 | GET | `/api/media` | `kind?`, `source?`, `channelId?`, `authorId?`, `aspect?`, `resolution?`, `after?`, `before?`, `limit?`, `offset?` | Media items across every scrape, newest first. `source` is `attachment`, `sticker`, or `embed`; `aspect` and `resolution` are the preset keys; `after`/`before` are ISO times on `posted_at`. Items carry `authorName`, `postedAt`, `width`, `height`, `aspectRatio`, `contentType`, `durationSecs`; `localUrl`/`thumbUrl` when a file or preview exists |
 | GET | `/api/media/:scrapeId/:itemId/file` | none | The downloaded file, content-typed from its extension |
 | GET | `/api/media/:scrapeId/:itemId/thumb` | none | The cached preview (type from `preview_ext`) |
-| GET | `/api/media/:scrapeId/:itemId/stream` | none | Playback/full-view source: the local file, or the remote URL refreshed from the source message. Supports `Range` |
+| GET | `/api/media/:scrapeId/:itemId/stream` | none | Playback/full-view source: the local file, or the remote URL refreshed from the source message. Supports `Range`. Non-media upstream responses (provider pages) return `415` |
 | GET | `/api/media/scrapes` | none | Every scrape with state and counters |
 | GET | `/api/media/status` | none | Slopbot connection state and the scrape list |
 | GET | `/api/media/authors` | none | Distinct posters across every scrape, with counts |
diff --git a/poc/public/media.js b/poc/public/media.js
index c863bf3..44090e6 100644
--- a/poc/public/media.js
+++ b/poc/public/media.js
@@ -424,6 +424,13 @@
         media.replaceChildren(el("span", "vk-media-card-kind", item.kind.toUpperCase()));
     }
 
+    /** Only real video files can be framed; embed pages (YouTube etc.) never are. */
+    function canFrameVideo(item) {
+        const direct = /\.(mp4|webm|m4v)(\?|$)/i;
+        if (item.playUrl && direct.test(item.playUrl)) return true;
+        return item.source !== "embed" && direct.test(item.url ?? "");
+    }
+
     function playIcon(item) {
         const play = el("span", "vk-media-play", "▶");
         play.title = "Play";
@@ -470,7 +477,7 @@
             }
 
             media.append(img);
-        } else if (item.kind === "video") {
+        } else if (item.kind === "video" && canFrameVideo(item)) {
             // No thumbnail: take the first frame through the same-origin stream endpoint,
             // which refreshes expired URLs and avoids cross-origin blocking.
             const video = document.createElement("video");
@@ -1160,14 +1167,14 @@
                     );
                     media.append(
                         button("Open in new tab", () =>
-                            window.open(directVideo, "_blank", "noreferrer")
+                            window.open(item.playUrl || directVideo, "_blank", "noreferrer")
                         )
                     );
                 },
                 { once: true }
             );
             media.append(video);
-        } else if (item.kind === "video") {
+        } else if (item.kind === "video" && canFrameVideo(item)) {
             // No still available: show the first frame through the stream endpoint.
             const video = document.createElement("video");
             video.preload = "metadata";
@@ -1183,7 +1190,7 @@
             );
             media.append(video);
             media.append(viewerPlayIcon(item));
-        } else if (/^(https?:|\/)/.test(source)) {
+        } else if ((item.kind === "image" || item.kind === "gif") && /^(https?:|\/)/.test(source)) {
             const img = document.createElement("img");
             img.src = source;
             img.alt = item.kind;
diff --git a/poc/src/webui.ts b/poc/src/webui.ts
index 05d3810..8591410 100644
--- a/poc/src/webui.ts
+++ b/poc/src/webui.ts
@@ -807,6 +807,13 @@ export function startWebUi(deps: WebUiDeps): WebUiHandle {
                 throw new HttpError(502, `upstream ${upstream.status}`);
             }
 
+            // Never pipe a page into a media element: embed URLs that are not direct files
+            // (YouTube, provider redirectors) answer with HTML.
+            const upstreamType = upstream.headers.get("content-type") ?? "";
+            if (!/^(image|video|audio|application\/octet-stream)/i.test(upstreamType)) {
+                throw new HttpError(415, `not a media resource (${upstreamType || "unknown"})`);
+            }
+
             res.status(upstream.status);
             for (const header of ["content-type", "content-length", "accept-ranges", "content-range"]) {
                 const value = upstream.headers.get(header);