diff --git a/packages/lint/src/rules/media.test.ts b/packages/lint/src/rules/media.test.ts
index 4435e8eb9b..1d621e8a51 100644
--- a/packages/lint/src/rules/media.test.ts
+++ b/packages/lint/src/rules/media.test.ts
@@ -796,3 +796,73 @@ describe("audio_carve_ungrouped_sources", () => {
     expect(finding?.severity).toBe("warning");
   });
 });
+
+describe("media_src_kind_mismatch", () => {
+  it("errors when <video> src is an image", async () => {
+    const html = `
+<html><body>
+  <div id="root" data-composition-id="c1" data-width="1920" data-height="1080">
+    <video id="bg" src="still.jpg" data-start="0" data-duration="5" muted></video>
+  </div>
+  <script>window.__timelines = {};</script>
+</body></html>`;
+    const result = await lintHyperframeHtml(html);
+    const finding = result.findings.find((f) => f.code === "media_src_kind_mismatch");
+    expect(finding?.severity).toBe("error");
+    expect(finding?.elementId).toBe("bg");
+    expect(finding?.message).toContain("image");
+  });
+
+  it("errors when <img> src is a video", async () => {
+    const html = `
+<html><body>
+  <div id="root" data-composition-id="c1" data-width="1920" data-height="1080">
+    <img id="still" src="clip.mov">
+  </div>
+  <script>window.__timelines = {};</script>
+</body></html>`;
+    const result = await lintHyperframeHtml(html);
+    const finding = result.findings.find((f) => f.code === "media_src_kind_mismatch");
+    expect(finding?.severity).toBe("error");
+    expect(finding?.elementId).toBe("still");
+    expect(finding?.message).toContain("video");
+  });
+
+  it("errors when <video> src is a data:image URI", async () => {
+    const html = `
+<html><body>
+  <div id="root" data-composition-id="c1" data-width="1920" data-height="1080">
+    <video src="data:image/png;base64,aaaa" data-start="0" muted></video>
+  </div>
+  <script>window.__timelines = {};</script>
+</body></html>`;
+    const result = await lintHyperframeHtml(html);
+    expect(result.findings.some((f) => f.code === "media_src_kind_mismatch")).toBe(true);
+  });
+
+  it("does not flag matching video/img src kinds", async () => {
+    const html = `
+<html><body>
+  <div id="root" data-composition-id="c1" data-width="1920" data-height="1080">
+    <video id="v1" src="clip.mp4" data-start="0" data-duration="5" muted></video>
+    <img id="i1" src="still.png">
+  </div>
+  <script>window.__timelines = {};</script>
+</body></html>`;
+    const result = await lintHyperframeHtml(html);
+    expect(result.findings.find((f) => f.code === "media_src_kind_mismatch")).toBeUndefined();
+  });
+
+  it("does not flag extensionless or audio src", async () => {
+    const html = `
+<html><body>
+  <div id="root" data-composition-id="c1" data-width="1920" data-height="1080">
+    <video id="v1" src="https://images.unsplash.com/photo-1566041510394" data-start="0" muted></video>
+    <audio id="a1" src="still.jpg" data-start="0"></audio>
+  </div>
+  <script>window.__timelines = {};</script>
+</body></html>`;
+    const result = await lintHyperframeHtml(html);
+    expect(result.findings.find((f) => f.code === "media_src_kind_mismatch")).toBeUndefined();
+  });
+});
diff --git a/packages/lint/src/rules/media.ts b/packages/lint/src/rules/media.ts
index 2346a81269..a2509ad09c 100644
--- a/packages/lint/src/rules/media.ts
+++ b/packages/lint/src/rules/media.ts
@@ -41,6 +41,90 @@ function hasAttrName(tagSource: string, attr: string): boolean {
   return new RegExp(`(?:^|\\s)${escaped}(?:\\s*=|\\s|/?>)`, "i").test(attrs);
 }
 
+const IMAGE_SRC_EXT = new Set([
+  "jpg",
+  "jpeg",
+  "png",
+  "gif",
+  "bmp",
+  "webp",
+  "svg",
+  "heic",
+  "heif",
+  "tiff",
+  "ico",
+]);
+const VIDEO_SRC_EXT = new Set([
+  "mp4",
+  "mov",
+  "avi",
+  "webm",
+  "mkv",
+  "flv",
+  "wmv",
+  "m4v",
+  "mpg",
+  "mpeg",
+]);
+
+function srcKind(src: string): "image" | "video" | null {
+  const stripped = src.trim();
+  if (!stripped) return null;
+  const lower = stripped.toLowerCase();
+  if (lower.startsWith("data:")) {
+    const mime = /^data:([^;,]+)/i.exec(stripped)?.[1]?.toLowerCase();
+    if (!mime) return null;
+    if (mime.startsWith("image/")) return "image";
+    if (mime.startsWith("video/")) return "video";
+    return null;
+  }
+  if (lower.startsWith("blob:")) return null;
+  let pathname = stripped;
+  try {
+    if (/^https?:/i.test(stripped)) {
+      pathname = decodeURIComponent(new URL(stripped).pathname);
+    } else {
+      pathname = stripped.split("?")[0]?.split("#")[0] ?? stripped;
+    }
+  } catch {
+    pathname = stripped.split("?")[0]?.split("#")[0] ?? stripped;
+  }
+  const base = pathname.split("/").pop() ?? "";
+  const dot = base.lastIndexOf(".");
+  if (dot < 0) return null;
+  const ext = base.slice(dot + 1).toLowerCase();
+  if (IMAGE_SRC_EXT.has(ext)) return "image";
+  if (VIDEO_SRC_EXT.has(ext)) return "video";
+  return null;
+}
+
+function findMediaSrcKindMismatchFindings(ctx: LintContext): HyperframeLintFinding[] {
+  const findings: HyperframeLintFinding[] = [];
+  for (const tag of ctx.tags) {
+    if (tag.name !== "video" && tag.name !== "img") continue;
+    const src = readAttr(tag.raw, "src");
+    if (!src) continue;
+    const kind = srcKind(src);
+    if (kind === null) continue;
+    if (tag.name === "video" && kind !== "image") continue;
+    if (tag.name === "img" && kind !== "video") continue;
+    const elementId = readAttr(tag.raw, "id") || undefined;
+    const expected = tag.name === "video" ? "video" : "image";
+    findings.push({
+      code: "media_src_kind_mismatch",
+      severity: "error",
+      message: `<${tag.name}${elementId ? ` id="${elementId}"` : ""}> src is a ${kind}, not a ${expected}. The producer fail-closes when the tag and file kind disagree.`,
+      elementId,
+      fixHint:
+        tag.name === "video"
+          ? "Use <img> for a still, or point <video> at a video URL (mp4/webm/mov/…)."
+          : "Use <video> for a video URL, or point <img> at a still (png/jpg/webp/…).",
+      snippet: truncateSnippet(tag.raw),
+    });
+  }
+  return findings;
+}
+
 /** Parent `src`, else a descendant `<source src>` (matches engine resolveMediaElementSrc). */
 function mediaHasResolvableSrc(tag: OpenTag, tags: readonly OpenTag[]): boolean {
   if (readAttr(tag.raw, "src")) return true;
@@ -459,6 +543,9 @@ export const mediaRules: Array<(ctx: LintContext) => HyperframeLintFinding[]> =
     return findings;
   },
 
+  // media_src_kind_mismatch
+  findMediaSrcKindMismatchFindings,
+
   // placeholder_media_url
   ({ tags }) => {
     const findings: HyperframeLintFinding[] = [];
