diff --git a/frontend/src/features/library/LibraryDetail.tsx b/frontend/src/features/library/LibraryDetail.tsx
index b5f8efa..4a1e2cd 100644
--- a/frontend/src/features/library/LibraryDetail.tsx
+++ b/frontend/src/features/library/LibraryDetail.tsx
@@ -708,10 +708,10 @@ export function LibraryDetail({ jId }: { jId: string }) {
             </p>
           </section>
 
-          <MatchCard key={item.j_id} item={item} canEdit={canEdit} />
+          <MatchCard key={`${item.j_id}-match`} item={item} canEdit={canEdit} />
 
           {user ? (
-            <IqdbCard key={item.j_id} item={item} canLink={canEdit} />
+            <IqdbCard key={`${item.j_id}-iqdb`} item={item} canLink={canEdit} />
           ) : null}
 
           <section className="rounded-lg border border-ctp-surface0 bg-ctp-base p-4">
diff --git a/frontend/src/features/optimize/video.ts b/frontend/src/features/optimize/video.ts
index 3906eca..820c0ef 100644
--- a/frontend/src/features/optimize/video.ts
+++ b/frontend/src/features/optimize/video.ts
@@ -8,7 +8,6 @@ import {
   StreamTarget,
   UrlSource,
   WebMOutputFormat,
-  getFirstEncodableVideoCodec,
   type StreamTargetChunk,
   type VideoCodec,
 } from "mediabunny";
@@ -125,18 +124,24 @@ export async function optimizeVideo(
   options: OptimizeOptions,
   report: ProgressReporter,
 ): Promise<OptimizeResult> {
+  if (typeof VideoEncoder === "undefined") {
+    throw new Error(
+      "This browser does not expose WebCodecs (VideoEncoder) inside workers.",
+    );
+  }
   const extension = extensionOf(filename);
   report(0.03, "Reading the video…");
-  const input = new Input({
+  const probe = new Input({
     source: new UrlSource(url, { maxCacheSize: 4 * 1024 * 1024 }),
     formats: ALL_FORMATS,
   });
-  const track = await input.getPrimaryVideoTrack();
+  const track = await probe.getPrimaryVideoTrack();
   if (!track) {
     throw new Error("No video track found in this file.");
   }
   const sourceWidth = await track.getDisplayWidth();
   const sourceHeight = await track.getDisplayHeight();
+  probe.dispose?.();
 
   const container: "mp4" | "webm" =
     options.container === "keep"
@@ -147,53 +152,69 @@ export async function optimizeVideo(
   const format =
     container === "webm" ? new WebMOutputFormat() : new Mp4OutputFormat();
 
+  const outputHeight = even(options.height ?? sourceHeight);
+  const outputWidth = even(
+    Math.round(sourceWidth * (outputHeight / sourceHeight)),
+  );
   const quality = new Quality(options.qualityLevel);
-  let codec: VideoCodec | undefined =
-    options.codec === "auto" ? undefined : options.codec;
-  if (!codec) {
-    const candidate = await getFirstEncodableVideoCodec(
-      CODEC_CANDIDATES[container],
-      { width: sourceWidth, height: sourceHeight, quality },
-    );
-    if (!candidate) {
-      throw new Error(
-        `This browser cannot encode ${container.toUpperCase()} video.`,
-      );
-    }
-    codec = candidate;
-  }
-
-  const outputHeight = options.height ?? sourceHeight;
-  const outputWidth = Math.round(sourceWidth * (outputHeight / sourceHeight));
-
-  const { target, toBlob } = createStreamOutput();
-  const output = new Output({ format, target });
+  const candidates: VideoCodec[] =
+    options.codec === "auto" ? CODEC_CANDIDATES[container] : [options.codec];
+  const preferences: ("prefer-hardware" | "no-preference")[] =
+    options.preferHardware ? ["prefer-hardware", "no-preference"] : ["no-preference"];
 
   report(0.06, "Preparing the encoder…");
-  const conversion = await Conversion.init({
-    input,
-    output,
-    video: {
-      codec,
-      quality,
-      height: even(outputHeight),
-      fit: "contain",
-      hardwareAcceleration: options.preferHardware
-        ? "prefer-hardware"
-        : "no-preference",
-      forceTranscode: true,
-    },
-  });
-  if (!conversion.isValid) {
+  let winner:
+    | {
+        conversion: Conversion;
+        input: Input;
+        stream: ReturnType<typeof createStreamOutput>;
+        codec: VideoCodec;
+      }
+    | null = null;
+  const tried: string[] = [];
+  for (const codec of candidates) {
+    for (const preference of preferences) {
+      tried.push(`${codec}${preference === "prefer-hardware" ? " (hw)" : ""}`);
+      const input = new Input({
+        source: new UrlSource(url, { maxCacheSize: 4 * 1024 * 1024 }),
+        formats: ALL_FORMATS,
+      });
+      const stream = createStreamOutput();
+      const output = new Output({ format, target: stream.target });
+      const attempt = await Conversion.init({
+        input,
+        output,
+        video: {
+          codec,
+          quality,
+          width: outputWidth,
+          height: outputHeight,
+          fit: "contain",
+          hardwareAcceleration: preference,
+          forceTranscode: true,
+        },
+      });
+      if (attempt.isValid) {
+        winner = { conversion: attempt, input, stream, codec };
+        break;
+      }
+      input.dispose?.();
+    }
+    if (winner) break;
+  }
+  if (!winner) {
     throw new Error(
-      "This conversion is not supported here — try another codec or container.",
+      `This browser could not configure ${container.toUpperCase()} encoding for ` +
+        `${outputWidth}×${outputHeight} (tried ${tried.join(", ")}). ` +
+        "Try another codec, container or resolution.",
     );
   }
-  conversion.onProgress = (progress: number) => {
+
+  winner.conversion.onProgress = (progress: number) => {
     report(0.08 + Math.min(Math.max(progress, 0), 1) * 0.85, "Encoding…");
   };
   try {
-    await conversion.execute();
+    await winner.conversion.execute();
   } catch (error) {
     throw new Error(
       `Video encoding failed: ${
@@ -201,14 +222,14 @@ export async function optimizeVideo(
       }`,
     );
   } finally {
-    input.dispose?.();
+    winner.input.dispose?.();
   }
 
   report(0.97, "Packaging…");
   return {
-    blob: toBlob(container === "webm" ? "video/webm" : "video/mp4"),
-    width: even(outputWidth),
-    height: even(outputHeight),
-    note: `${codec} · ${container}`,
+    blob: winner.stream.toBlob(container === "webm" ? "video/webm" : "video/mp4"),
+    width: outputWidth,
+    height: outputHeight,
+    note: `${winner.codec} · ${container}`,
   };
 }