diff --git a/web/packages/gallery/services/ffmpeg/web.ts b/web/packages/gallery/services/ffmpeg/web.ts
index 890bdd9882..f1b9a6912c 100644
--- a/web/packages/gallery/services/ffmpeg/web.ts
+++ b/web/packages/gallery/services/ffmpeg/web.ts
@@ -44,23 +44,17 @@ const createFFmpeg = async () => {
  *
  * @param blob The input data on which to run the command, provided as a blob.
  *
- * @param outputFileExtension The extension(s) of the (temporary) output file
- * which will be generated by the command. If multiple of these are provided,
- * then the first one is used for the OUTPUT placeholder, while the rest of them
- * are expected to have been generated by the ffmpeg command implicitly.
+ * @param outputFileExtension The extension of the (temporary) output file which
+ * will be generated by the command.
  *
- * @returns The contents (bytes as {@link Uint8Array}) of the output file
- * generated as a result of executing {@link command} on {@link blob}. If a
- * single {@link outputFileExtension} is provided, then the result will be a
- * single {@link Uint8Array}, otherwise it will be an array of
- * {@link Uint8Array}, one for each entry in {@link outputFileExtension}
- * respectively.
+ * @returns The contents of the output file generated as a result of executing
+ * {@link command} on {@link blob}.
  */
-export const ffmpegExecWeb = async <T extends string | string[]>(
+export const ffmpegExecWeb = async (
     command: string[],
     blob: Blob,
-    outputFileExtension: T,
-): Promise<T extends string ? Uint8Array : Uint8Array[]> => {
+    outputFileExtension: string,
+): Promise<Uint8Array> => {
     const ffmpeg = await ffmpegLazy();
     // Interleaving multiple ffmpeg.execs causes errors like
     //
@@ -72,20 +66,14 @@ export const ffmpegExecWeb = async <T extends string | string[]>(
     );
 };
 
-const ffmpegExec = async <T extends string | string[]>(
+const ffmpegExec = async (
     ffmpeg: FFmpeg,
     command: string[],
-    outputFileExtension: T,
+    outputFileExtension: string,
     blob: Blob,
-): Promise<T extends string ? Uint8Array : Uint8Array[]> => {
+) => {
     const inputPath = newID("in_");
-    const firstOutputFileExtension =
-        typeof outputFileExtension == "string"
-            ? outputFileExtension
-            : outputFileExtension[0];
-    const outputSuffix = firstOutputFileExtension
-        ? "." + firstOutputFileExtension
-        : "";
+    const outputSuffix = outputFileExtension ? "." + outputFileExtension : "";
     const outputPath = newID("out_") + outputSuffix;
 
     const cmd = substitutePlaceholders(command, inputPath, outputPath);
@@ -109,17 +97,12 @@ const ffmpegExec = async <T extends string | string[]>(
             throw new Error(`ffmpeg command failed with exit code ${status}`);
         }
 
-        if (typeof outputFileExtension == "string") {
-            const result = await ffmpeg.readFile(outputPath);
-            if (typeof result == "string")
-                throw new Error("Expected binary data");
+        const result = await ffmpeg.readFile(outputPath);
+        if (typeof result == "string") throw new Error("Expected binary data");
 
-            const ms = Date.now() - startTime;
-            log.debug(() => `[wasm] ffmpeg ${cmd.join(" ")} (${ms} ms)`);
-            return result;
-        } else {
-            return [] as Uint8Array[];
-        }
+        const ms = Date.now() - startTime;
+        log.debug(() => `[wasm] ffmpeg ${cmd.join(" ")} (${ms} ms)`);
+        return result;
     } finally {
         try {
             await ffmpeg.deleteFile(inputPath);