fix: order user-facing stems

Author: hi-ogawa-agent

packages/app/src/app.tsx

@@ -15,7 +15,6 @@ import type { SeparateRequest } from "./lib/audio/separate";
 import {
   createStemArchive,
   downloadBlob,
-  orderStemFiles,
   toStemArchiveFilename,
 } from "./lib/audio/stem-archive";
 import { encodeWavF32 } from "./lib/audio/wav";
@@ -152,8 +151,7 @@ export function App() {
             progress ? updateRunProgress(progress, event, at) : progress,
           ),
       });
-      const orderedOutputs = orderStemFiles(separated, twoStems);
-      const nextOutputs = orderedOutputs.map((output) => {
+      const nextOutputs = separated.map((output) => {
         const blob = encodeWavF32(
           [output.left, output.right],
           AUDIO_SAMPLE_RATE,

packages/app/src/lib/audio/separate.ts

@@ -11,7 +11,6 @@ import {
   MODEL_INPUT_LENGTH,
   MODEL_OUTPUT_LENGTH,
   MODEL_SEGMENT,
-  SOURCES,
 } from "./constants";
 import { readModelFile, type ModelFilename, type ModelSource } from "./models";
 
@@ -151,12 +150,18 @@ export async function separate(
     req.right,
     host,
   );
-  const names = req.twoStems
-    ? [req.twoStems.source, `no_${req.twoStems.source}`]
-    : SOURCES;
-  return names.map((name, index) => ({
+  const stem = (name: string, index: number): SeparatedStem => ({
     name,
     left: tracks[2 * index],
     right: tracks[2 * index + 1],
-  }));
+  });
+  if (req.twoStems) {
+    return [stem(`no_${req.twoStems.source}`, 1), stem(req.twoStems.source, 0)];
+  }
+  return [
+    stem("vocals", 3),
+    stem("drums", 0),
+    stem("bass", 1),
+    stem("other", 2),
+  ];
 }

packages/app/src/lib/audio/stem-archive.ts

@@ -5,22 +5,6 @@ export interface StemFile {
   blob: Blob;
 }
 
-export function orderStemFiles<T extends { name: string }>(
-  stems: T[],
-  twoStemSource: string | null,
-): T[] {
-  if (!twoStemSource) {
-    return stems;
-  }
-
-  const order = [`no_${twoStemSource}`, twoStemSource];
-  const rank = (name: string) => {
-    const index = order.indexOf(name);
-    return index === -1 ? order.length : index;
-  };
-  return [...stems].sort((a, b) => rank(a.name) - rank(b.name));
-}
-
 export function toStemArchiveFilename(inputFilename: string): string {
   const basename = inputFilename.replaceAll(".", "_");
   return `${basename || "demucs"}.stems.zip`;