diff --git a/server/src/__tests__/issue-attachment-routes.test.ts b/server/src/__tests__/issue-attachment-routes.test.ts
index 7b1f57a5..4bcb2410 100644
--- a/server/src/__tests__/issue-attachment-routes.test.ts
+++ b/server/src/__tests__/issue-attachment-routes.test.ts
@@ -412,6 +412,25 @@ describe("issue attachment routes", () => {
     );
   });
 
+  it("serves mp4 attachments inline when stored with a generic binary content type", async () => {
+    const storage = createStorageService(Buffer.from("abcdef"));
+    mockIssueService.getAttachmentById.mockResolvedValue({
+      ...makeAttachment("application/octet-stream", "clip.mp4"),
+      byteSize: 6,
+    });
+
+    const app = await createApp(storage);
+    const res = await request(app)
+      .get("/api/attachments/attachment-1/content")
+      .set("Range", "bytes=1-3");
+
+    expect(res.status).toBe(206);
+    expect(res.headers["content-type"]).toContain("video/mp4");
+    expect(res.headers["content-disposition"]).toBe('inline; filename="clip.mp4"');
+    expect(res.headers["content-range"]).toBe("bytes 1-3/6");
+    expect(Buffer.from(res.body).toString("utf8")).toBe("bcd");
+  });
+
   it("forces video downloads when the download path is requested", async () => {
     const storage = createStorageService();
     mockIssueService.getAttachmentById.mockResolvedValue(makeAttachment("video/webm", "clip.webm"));
diff --git a/server/src/routes/issues.ts b/server/src/routes/issues.ts
index ba07190f..85492638 100644
--- a/server/src/routes/issues.ts
+++ b/server/src/routes/issues.ts
@@ -185,6 +185,30 @@ function buildAttachmentContentPath(attachmentId: string): string {
   return `/api/attachments/${attachmentId}/content`;
 }
 
+const GENERIC_ATTACHMENT_CONTENT_TYPES = new Set([
+  "application/octet-stream",
+  "binary/octet-stream",
+  "application/x-binary",
+]);
+
+function inferVideoContentTypeFromFilename(filename: string | null | undefined): string | null {
+  const lower = (filename ?? "").toLowerCase();
+  if (lower.endsWith(".mp4") || lower.endsWith(".m4v")) return "video/mp4";
+  if (lower.endsWith(".webm")) return "video/webm";
+  if (lower.endsWith(".mov") || lower.endsWith(".qt") || lower.endsWith(".quicktime")) return "video/quicktime";
+  return null;
+}
+
+function resolveAttachmentResponseContentType(input: {
+  storedContentType: string | null | undefined;
+  objectContentType?: string | null;
+  originalFilename?: string | null;
+}) {
+  const storedContentType = normalizeContentType(input.storedContentType || input.objectContentType);
+  if (!GENERIC_ATTACHMENT_CONTENT_TYPES.has(storedContentType)) return storedContentType;
+  return inferVideoContentTypeFromFilename(input.originalFilename) ?? storedContentType;
+}
+
 function requiresPaperclipAttachmentMetadata(input: {
   type?: unknown;
   provider?: unknown;
@@ -6267,7 +6291,11 @@ export function issueRoutes(
       attachment.objectKey,
       range.kind === "range" ? { range: { start: range.start, end: range.end } } : undefined,
     );
-    const responseContentType = normalizeContentType(attachment.contentType || object.contentType);
+    const responseContentType = resolveAttachmentResponseContentType({
+      storedContentType: attachment.contentType,
+      objectContentType: object.contentType,
+      originalFilename: attachment.originalFilename,
+    });
     res.setHeader("Content-Type", responseContentType);
     res.setHeader("Cache-Control", "private, max-age=60");
     res.setHeader("X-Content-Type-Options", "nosniff");
diff --git a/ui/src/components/IssueAttachmentsSection.test.tsx b/ui/src/components/IssueAttachmentsSection.test.tsx
index 7cec72e6..4e54e05f 100644
--- a/ui/src/components/IssueAttachmentsSection.test.tsx
+++ b/ui/src/components/IssueAttachmentsSection.test.tsx
@@ -155,6 +155,33 @@ describe("IssueAttachmentsSection", () => {
     expect(fetchSpy).not.toHaveBeenCalled();
   });
 
+  it("treats mp4 filenames as playable videos even with a generic binary content type", async () => {
+    const attachment = makeAttachment({
+      id: "misclassified-mp4",
+      originalFilename: "demo.mp4",
+      contentType: "application/octet-stream",
+      contentPath: "/api/attachments/misclassified-mp4/content",
+    });
+
+    await act(async () => {
+      root.render(
+        <QueryClientProvider client={queryClient}>
+          <IssueAttachmentsSection
+            attachments={[attachment]}
+            onDelete={vi.fn()}
+            onImageClick={vi.fn()}
+          />
+        </QueryClientProvider>,
+      );
+    });
+    await flushReact();
+
+    const video = container.querySelector("video");
+    expect(video?.getAttribute("src")).toBe("/api/attachments/misclassified-mp4/content");
+    expect(container.textContent).toContain("application/octet-stream");
+    expect(fetchSpy).not.toHaveBeenCalled();
+  });
+
   it("keeps generic attachments as compact file rows with open and download actions", async () => {
     const attachment = makeAttachment({
       id: "pdf-attachment",
diff --git a/ui/src/lib/issue-attachments.ts b/ui/src/lib/issue-attachments.ts
index b9dc1565..29219c46 100644
--- a/ui/src/lib/issue-attachments.ts
+++ b/ui/src/lib/issue-attachments.ts
@@ -25,8 +25,20 @@ export function isImageAttachment(attachment: Pick<IssueAttachment, "contentType
   return normalizedContentType(attachment).startsWith("image/");
 }
 
-export function isVideoAttachment(attachment: Pick<IssueAttachment, "contentType">) {
-  return isVideoContentType(normalizedContentType(attachment));
+export function isVideoAttachment(
+  attachment: Pick<IssueAttachment, "contentType" | "originalFilename">,
+) {
+  if (isVideoContentType(normalizedContentType(attachment))) return true;
+
+  const filename = (attachment.originalFilename ?? "").toLowerCase();
+  return (
+    filename.endsWith(".mp4") ||
+    filename.endsWith(".m4v") ||
+    filename.endsWith(".webm") ||
+    filename.endsWith(".mov") ||
+    filename.endsWith(".qt") ||
+    filename.endsWith(".quicktime")
+  );
 }
 
 export function isMarkdownAttachment(