diff --git a/electron/ipc/handlers/__tests__/demo.handlers.test.ts b/electron/ipc/handlers/__tests__/demo.handlers.test.ts
index 633a0ff86..31b98f7c9 100644
--- a/electron/ipc/handlers/__tests__/demo.handlers.test.ts
+++ b/electron/ipc/handlers/__tests__/demo.handlers.test.ts
@@ -22,7 +22,7 @@ const fsMock = vi.hoisted(() => ({
 vi.mock("fs/promises", () => fsMock);
 
 vi.mock("fs", () => ({
-  readdirSync: vi.fn(() => ["frame_0001.png", "frame_0002.png", "frame_0003.png"]),
+  readdirSync: vi.fn(() => ["frame-000001.png", "frame-000002.png", "frame-000003.png"]),
   mkdirSync: vi.fn(),
 }));
 
@@ -196,7 +196,27 @@ describe("registerDemoHandlers", () => {
           outputPath: "/tmp/out.mp4",
           preset: "youtube-4k",
         })
-      ).rejects.toThrow("No PNG frames matching frame_NNNN.png found");
+      ).rejects.toThrow("No PNG frames matching frame-NNNNNN.png found");
+    });
+
+    it("rejects old underscore-format frame names", async () => {
+      const fsMod = await import("fs");
+      (fsMod.readdirSync as ReturnType<typeof vi.fn>).mockReturnValueOnce([
+        "frame_0001.png",
+        "frame_0002.png",
+        "frame_0003.png",
+      ]);
+
+      const handler = getEncodeHandler();
+      const event = makeEvent();
+
+      await expect(
+        handler(event, {
+          framesDir: "/tmp/old-format",
+          outputPath: "/tmp/out.mp4",
+          preset: "youtube-4k",
+        })
+      ).rejects.toThrow("No PNG frames matching frame-NNNNNN.png found");
     });
 
     it("rejects on spawn error event", async () => {
@@ -303,7 +323,7 @@ describe("registerDemoHandlers", () => {
 
       expect(spawnMock).toHaveBeenCalledWith(
         expect.any(String),
-        expect.arrayContaining(["-c:v", "libx264"]),
+        expect.arrayContaining(["-i", "/tmp/frames/frame-%06d.png", "-c:v", "libx264"]),
         expect.any(Object)
       );
     });
diff --git a/electron/ipc/handlers/demo.ts b/electron/ipc/handlers/demo.ts
index 3d3851e57..2dfe3541a 100644
--- a/electron/ipc/handlers/demo.ts
+++ b/electron/ipc/handlers/demo.ts
@@ -315,20 +315,20 @@ export function registerDemoHandlers(deps: HandlerDependencies): () => void {
     const { framesDir, outputPath, preset, fps = 30 } = payload;
     const presetConfig = ENCODE_PRESETS[preset];
 
-    const framePattern = /^frame_\d{4}\.png$/;
+    const framePattern = /^frame-\d{6}\.png$/;
     const pngFiles = fs
       .readdirSync(framesDir)
       .filter((f) => framePattern.test(f))
       .sort();
     if (pngFiles.length === 0) {
-      throw new Error(`No PNG frames matching frame_NNNN.png found in ${framesDir}`);
+      throw new Error(`No PNG frames matching frame-NNNNNN.png found in ${framesDir}`);
     }
     const totalFrames = pngFiles.length;
 
     fs.mkdirSync(path.dirname(outputPath), { recursive: true });
 
     const startTime = Date.now();
-    const inputPattern = path.join(framesDir, "frame_%04d.png");
+    const inputPattern = path.join(framesDir, "frame-%06d.png");
 
     const args = [
       "-y",