diff --git a/services/worker/src/workers/conform.js b/services/worker/src/workers/conform.js
index 2c4e8c4..77cb3fc 100644
--- a/services/worker/src/workers/conform.js
+++ b/services/worker/src/workers/conform.js
@@ -85,7 +85,15 @@ export const conformWorker = async (job) => {
   const tmpDir = tmpdir();
   const segmentsDir = join(tmpDir, `segments-${jobId}`);
   const segmentListPath = join(tmpDir, `segments-${jobId}.txt`);
-  const outputPath = join(tmpDir, `output-${jobId}.mp4`);
+  // Container per codec — ProRes / DNxHR live in QuickTime (MOV); MP4 only
+  // accepts H.264/H.265 and a handful of others. The earlier .mp4 hard-code
+  // tripped ffmpeg with:
+  //   [mp4] Could not find tag for codec prores in stream #0,
+  //          codec not currently supported in container
+  const outputExt =
+    (codec === 'prores' || codec === 'prores_hq' || codec === 'prores_4444' || codec === 'dnxhr_hq')
+      ? 'mov' : 'mp4';
+  const outputPath = join(tmpDir, `output-${jobId}.${outputExt}`);
 
   try {
     let edits = [];
@@ -319,7 +327,7 @@ export const conformWorker = async (job) => {
     ]);
 
     await job.updateProgress(85);
-    const outputKey = `jobs/${jobId}/conformed.mp4`;
+    const outputKey = `jobs/${jobId}/conformed.${outputExt}`;
     console.log(`[conform] Uploading output to ${outputKey}`);
     await uploadToS3(S3_BUCKET, outputKey, outputPath);
 
@@ -329,7 +337,7 @@ export const conformWorker = async (job) => {
        VALUES ($1, $2, $3, 'video', 'ready', $4, $5, $6, $7, $8, $9) RETURNING id`,
       [
         projectId || null,
-        `conformed-${seqName.replace(/[^a-z0-9]/gi, '_')}.mp4`,
+        `conformed-${seqName.replace(/[^a-z0-9]/gi, '_')}.${outputExt}`,
         `Conformed: ${seqName}`,
         outputKey,
         // Normalise the panel's codec id into the canonical name we store on