diff --git a/src/N_m3u8DL-RE/Util/MergeUtil.cs b/src/N_m3u8DL-RE/Util/MergeUtil.cs
index 3f7e2e0..5917e5b 100644
--- a/src/N_m3u8DL-RE/Util/MergeUtil.cs
+++ b/src/N_m3u8DL-RE/Util/MergeUtil.cs
@@ -151,7 +151,7 @@ namespace N_m3u8DL_RE.Util
                     command.Append("\" -map 0  -c copy -y " + (useAACFilter ? "-bsf:a aac_adtstoasc" : "") + " \"" + outputPath + ".flv\"");
                     break;
                 case ("M4A"):
-                    command.Append("\" -map 0  -c copy -y " + (useAACFilter ? "-bsf:a aac_adtstoasc" : "") + " \"" + outputPath + ".m4a\"");
+                    command.Append("\" -map 0  -c copy -f mp4 -y " + (useAACFilter ? "-bsf:a aac_adtstoasc" : "") + " \"" + outputPath + ".m4a\"");
                     break;
                 case ("TS"):
                     command.Append("\" -map 0  -c copy -y -f mpegts -bsf:v h264_mp4toannexb \"" + outputPath + ".ts\"");