diff --git a/public/index.html b/public/index.html
index ac236f5..6609ff6 100644
--- a/public/index.html
+++ b/public/index.html
@@ -1083,12 +1083,14 @@ async function uploadHTTP(files) {
     try {
       const presigned = await api('POST','/api/presigned',{filename:item.name,prefix:selectedPrefix,contentType:item.file.type||'application/octet-stream'});
       if (!presigned.success) throw new Error(presigned.error||'Failed to get presigned URL');
+      // Use the content type the server signed — browser file.type may differ for broadcast formats
+      const signedType = presigned.contentType || item.file.type || 'application/octet-stream';
       await new Promise((resolve,reject) => {
         const xhr=new XMLHttpRequest();
         xhr.open('PUT',presigned.url);
-        xhr.setRequestHeader('Content-Type',item.file.type||'application/octet-stream');
+        xhr.setRequestHeader('Content-Type',signedType);
         xhr.upload.onprogress=e=>{ if(e.lengthComputable){ const p=Math.round(e.loaded/e.total*100); document.getElementById(`progbar-${idx}`).style.width=p+'%'; setFileStatus(idx,'uploading',p+'%'); } };
-        xhr.onload=()=>xhr.status<300?resolve():reject(new Error(`S3 ${xhr.status}`));
+        xhr.onload=()=>xhr.status<300?resolve():reject(new Error(`S3 error ${xhr.status}`));
         xhr.onerror=()=>reject(new Error('Network error'));
         xhr.send(item.file);
       });