refactor: rename two-stem complement output to backing across CLI, WASM, and web app (#61)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: Copilot

.github/workflows/ci.yml

@@ -62,7 +62,7 @@ jobs:
             --two-stems-mix minus \
             fixtures/sine-10s.wav data/ci-output/native
           test -s data/ci-output/native/bass.wav
-          test -s data/ci-output/native/no_bass.wav
+          test -s data/ci-output/native/backing.wav
 
       - run: pnpm build-wasm
 

README.md

@@ -39,7 +39,7 @@ pnpm model-release download models-2026-07-11 htdemucs_ft_bass
 pnpm cli-separate --name htdemucs_ft --two-stems bass --two-stems-mix minus data/input/song.wav data/output/song
 ```
 
-This creates `bass.wav` and `no_bass.wav`.
+This creates `bass.wav` and `backing.wav`.
 
 Run the same separation flow through the Rust/WASM driver and
 `onnxruntime-web`'s Node WASM runtime with:

crates/cli/src/main.rs

@@ -129,7 +129,7 @@ fn separate(args: SeparateArgs) -> Result<()> {
             complement,
         } => vec![
             (source.name().to_string(), target),
-            (format!("no_{}", source.name()), complement),
+            ("backing".to_string(), complement),
         ],
     };
     std::fs::create_dir_all(&args.out_dir)?;

crates/core/src/lib.rs

@@ -83,7 +83,7 @@ impl Source {
 }
 
 /// What a separation yields, exactly; each track is stereo, `[channel][sample]`.
-/// How tracks are spelled (e.g. `no_bass.wav`) is the driver's concern.
+/// How tracks are spelled (e.g. `backing.wav`) is the driver's concern.
 pub enum Outputs {
     /// All four stems, in [`Source::ALL`] order.
     Full([[Vec<f32>; CHANNELS]; NUM_SOURCES]),

packages/app/e2e/preferences.spec.ts

@@ -19,7 +19,7 @@ test("restores and updates configuration preferences", async ({ page }) => {
   await expect(page.locator("#method")).toHaveValue("minus");
   await expect(page.locator("#method")).toBeEnabled();
   await expect(page.locator("#outputSummary")).toContainText(
-    "Creates bass.wav and no_bass.wav.",
+    "Creates bass.wav and backing.wav.",
   );
   await expect(page.locator("#shifts")).toHaveValue("3");
   await expect(page.getByLabel("Select htdemucs_ft_bass.onnx")).toBeAttached();

packages/app/src/app.tsx

@@ -355,7 +355,7 @@ export function App() {
                   {twoStems ? (
                     <>
                       Creates <strong>{twoStems}.wav</strong> and{" "}
-                      <strong>no_{twoStems}.wav</strong>.
+                      <strong>backing.wav</strong>.
                     </>
                   ) : (
                     <>
@@ -481,7 +481,7 @@ export function App() {
                   key={output.name}
                 >
                   <b className="text-xl font-semibold capitalize">
-                    {output.name}
+                    {stemLabel(output.name, twoStems)}
                   </b>
                   <audio
                     className="col-span-full w-full"
@@ -505,6 +505,13 @@ export function App() {
   );
 }
 
+function stemLabel(name: string, source: string | null): string {
+  if (name === "backing" && source) {
+    return `Backing track (without ${source})`;
+  }
+  return name;
+}
+
 function ModelFileSlot({
   filename,
   ready,

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

@@ -152,7 +152,7 @@ export async function separate(
   );
   const stemOrder: { name: string; index: number }[] = req.twoStems
     ? [
-        { name: `no_${req.twoStems.source}`, index: 1 },
+        { name: "backing", index: 1 },
         { name: req.twoStems.source, index: 0 },
       ]
     : [

packages/app/src/node/cli.ts

@@ -154,9 +154,7 @@ async function main() {
     right,
     host,
   );
-  const names = args.twoStems
-    ? [args.twoStems, `no_${args.twoStems}`]
-    : SOURCES;
+  const names = args.twoStems ? [args.twoStems, "backing"] : SOURCES;
   await mkdir(args.outDir, { recursive: true });
   for (const [index, name] of names.entries()) {
     const path = join(args.outDir, `${name}.wav`);