From 19258ea5ba47067e9d5756b122051c467ece0b04 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miguel=20=C3=81ngel?= <miguel.sierra@heygen.com>
Date: Sat, 18 Jul 2026 19:13:00 +0000
Subject: [PATCH] fix(render): cap final mux to video duration

---
 packages/engine/src/services/chunkEncoder.ts                | 5 +++++
 packages/producer/src/services/distributed/assemble.ts      | 6 +++++-
 .../producer/src/services/render/stages/assembleStage.ts    | 1 +
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/packages/engine/src/services/chunkEncoder.ts b/packages/engine/src/services/chunkEncoder.ts
index e30272644..a2d301781 100644
--- a/packages/engine/src/services/chunkEncoder.ts
+++ b/packages/engine/src/services/chunkEncoder.ts
@@ -79,6 +79,8 @@ export interface MuxVideoWithAudioOptions extends Partial<
   audioCodec?: "aac";
   /** Preserve a priming edit list known to have been created by AAC re-encoding. */
   preserveAudioPrimingEditList?: boolean;
+  /** Hard cap copied audio to the already-encoded video's exact duration. */
+  durationSeconds?: number;
 }
 
 async function shouldCopyAacSidecar(
@@ -706,6 +708,9 @@ export async function muxVideoWithAudio(
     // output container metadata. `-c:v copy` is retained; no re-encode.
     args.push("-r", fpsToFfmpegArg(fps));
   }
+  if (config?.durationSeconds !== undefined) {
+    args.push("-t", String(config.durationSeconds));
+  }
   args.push("-y", outputPath);
 
   const processTimeout = config?.ffmpegProcessTimeout ?? DEFAULT_CONFIG.ffmpegProcessTimeout;
diff --git a/packages/producer/src/services/distributed/assemble.ts b/packages/producer/src/services/distributed/assemble.ts
index df1f93c64..91f56ed90 100644
--- a/packages/producer/src/services/distributed/assemble.ts
+++ b/packages/producer/src/services/distributed/assemble.ts
@@ -323,7 +323,11 @@ export async function assemble(
         audioForMux,
         muxOutputPath,
         abortSignal,
-        { audioCodec: "aac", preserveAudioPrimingEditList },
+        {
+          audioCodec: "aac",
+          preserveAudioPrimingEditList,
+          durationSeconds: padTrimResult.targetDurationSeconds,
+        },
         { num: plan.dimensions.fpsNum, den: plan.dimensions.fpsDen },
       );
       if (!muxResult.success) {
diff --git a/packages/producer/src/services/render/stages/assembleStage.ts b/packages/producer/src/services/render/stages/assembleStage.ts
index ab218249b..6a2adf483 100644
--- a/packages/producer/src/services/render/stages/assembleStage.ts
+++ b/packages/producer/src/services/render/stages/assembleStage.ts
@@ -79,6 +79,7 @@ export async function runAssembleStage(input: AssembleStageInput): Promise<Assem
       {
         audioCodec: "aac",
         preserveAudioPrimingEditList: normalizeResult.operation === "trim",
+        durationSeconds: normalizeResult.targetDurationSeconds,
       },
       job.config.fps,
     );