fix(render): cap trimmed audio container duration

packages/producer/src/services/render/audioPadTrim.test.ts

@@ -91,6 +91,7 @@ describe("buildPadTrimAudioArgs", () => {
     expect(operation).toBe("trim");
     const filterIdx = args.indexOf("-af");
     expect(args[filterIdx + 1]).toBe("atrim=duration=15.000000,asetpts=PTS-STARTPTS");
+    expect(args[args.indexOf("-t") + 1]).toBe("15.000000");
     const codecIdx = args.indexOf("-c:a");
     expect(args[codecIdx + 1]).toBe("aac");
     expect(args[args.indexOf("-b:a") + 1]).toBe("192k");

packages/producer/src/services/render/audioPadTrim.ts

@@ -201,6 +201,12 @@ export function buildPadTrimAudioPlan(
           audioPath,
           "-af",
           `atrim=duration=${targetSec},asetpts=PTS-STARTPTS`,
+          // `atrim` limits decoded samples but does not cap muxer timestamps
+          // introduced by encoder delay/flush.  The output duration contract
+          // is enforced at the container boundary as well; without `-t`, a
+          // long primed source can retain its original tail after re-encode.
+          "-t",
+          targetSec,
           "-c:a",
           "aac",
           "-b:a",