diff --git a/packages/producer/src/services/render/audioPadTrim.test.ts b/packages/producer/src/services/render/audioPadTrim.test.ts
index 90fe862b4..4f79ac5bf 100644
--- a/packages/producer/src/services/render/audioPadTrim.test.ts
+++ b/packages/producer/src/services/render/audioPadTrim.test.ts
@@ -30,7 +30,8 @@ describe("buildPadTrimAudioArgs", () => {
     expect(plan.steps).toHaveLength(1);
     const args = plan.steps[0]!.args;
     expect(args[args.indexOf("-i") + 1]).toBe("/tmp/in.aac");
-    expect(args[args.indexOf("-af") + 1]).toBe("apad=whole_dur=5.000000");
+    expect(args[args.indexOf("-af") + 1]).toBe("apad,atrim=0:5.000000");
+    expect(args.join(" ")).not.toContain("whole_dur");
     expect(args[args.indexOf("-t") + 1]).toBe("5.000000");
     expect(args[args.indexOf("-c:a") + 1]).toBe("aac");
     // The single-step filter plan has no intermediate artifacts to clean up.
@@ -92,13 +93,9 @@ describe("buildPadTrimAudioArgs", () => {
     expect(trimNeeded.operation).toBe("trim");
   });
 
-  it("uses apad for Windows-safe duration normalization", () => {
-    // Regression pin for field-signal reports ts=1784169914 / 1784177061 /
-    // ts=1784177375 (win32/x64, CLI 0.7.59, ffmpeg 8.1.1-full_build). The
-    // concat demuxer's file open on Windows in FFmpeg 8.x rejects
-    // `file:///C:/…` URLs with "Impossible to open …". The concat script
-    // MUST use bare paths. Match sibling `assemble.ts` /
-    // `chunkEncoder.ts` conventions.
+  it("uses the portable apad/atrim filter for Windows duration normalization", () => {
+    // Bundled Windows FFmpeg builds reject `apad=whole_dur`. Match the
+    // portable finite-padding shape used by the main audio mixer.
     const winPlan = buildPadTrimAudioPlan(
       "C:\\Users\\alice\\AppData\\Local\\Temp\\hf-render-abc\\audio.aac",
       "C:\\Users\\alice\\AppData\\Local\\Temp\\hf-render-abc\\audio-padded.aac",
@@ -108,7 +105,8 @@ describe("buildPadTrimAudioArgs", () => {
     expect(winPlan.operation).toBe("pad");
     const args = winPlan.steps[0]!.args;
     expect(args).toContain("-af");
-    expect(args[args.indexOf("-af") + 1]).toBe("apad=whole_dur=5.000000");
+    expect(args[args.indexOf("-af") + 1]).toBe("apad,atrim=0:5.000000");
+    expect(args.join(" ")).not.toContain("whole_dur");
   });
 });
 
diff --git a/packages/producer/src/services/render/audioPadTrim.ts b/packages/producer/src/services/render/audioPadTrim.ts
index 6d56cec77..9aa30503f 100644
--- a/packages/producer/src/services/render/audioPadTrim.ts
+++ b/packages/producer/src/services/render/audioPadTrim.ts
@@ -142,7 +142,7 @@ export function buildPadTrimAudioPlan(
             "-i",
             audioPath,
             "-af",
-            `apad=whole_dur=${targetSec}`,
+            `apad,atrim=0:${targetSec}`,
             "-t",
             targetSec,
             "-c:a",
@@ -280,10 +280,6 @@ export async function padOrTrimAudioToVideoFrameCount(
 
   try {
     for (const step of plan.steps) {
-      // Materialize the concat-demuxer script to a real file when the step
-      // needs one. Doing this here (instead of piping via `pipe:0` in the
-      // runner) is what makes the demuxer's URL resolution treat
-      // absolute paths as absolute — see `concatFileLine` for context.
       const ffmpegResult = await runner(step.args);
       if (!ffmpegResult.success) {
         return {