diff --git a/build.sh b/build.sh
index 947d233..40c10d9 100644
--- a/build.sh
+++ b/build.sh
@@ -5,7 +5,7 @@ rm -rf dist
 pip uninstall pyutube -y
 
 # Build a wheel distribution package using the 'setup.py' file
-python setup.py sdist bdist_wheel
+python3 setup.py sdist bdist_wheel
 
 # Install the wheel distribution package located in the 'dist' directory
 # pip3 install dist/*
diff --git a/pyutube/services/DownloadService.py b/pyutube/services/DownloadService.py
index b0b51bf..070ed5a 100644
--- a/pyutube/services/DownloadService.py
+++ b/pyutube/services/DownloadService.py
@@ -75,7 +75,6 @@ def download_video(self, video: YouTube, video_id: str, video_stream: YouTube, v
         video_filename = self.file_service.generate_filename(video_stream, video_id)
 
         # Prepend the title number and `__` to the filename if ordering is required
-
         if self.make_playlist_in_order:
             video_base_name, video_extension = os.path.splitext(video_filename)
             video_filename = f"{title_number}__{video_base_name}{video_extension}"
diff --git a/pyutube/services/FileService.py b/pyutube/services/FileService.py
index 70bbfc8..6210a27 100644
--- a/pyutube/services/FileService.py
+++ b/pyutube/services/FileService.py
@@ -8,7 +8,6 @@
 
 
 class FileService:
-
     def save_file(self, video: YouTube, filename: str, path: str) -> None:
         """
         Save the file to the specified path with the given filename.
@@ -32,12 +31,10 @@ def generate_filename(self, video, video_id, is_audio=False, filename: str = "")
         """
         file_type = 'audio' if is_audio else video.resolution
 
-        extension = 'mp3' if is_audio else video.mime_type.split('/')[1]
-
         title = filename if filename != "" else video.default_filename.split('.')[0]
         title = safe_filename(title)
 
-        return f"{title} - {file_type}_-_{video_id}.{extension}"
+        return f"{title} - {file_type}_-_{video_id}"
 
     def handle_existing_file(
             self, video: YouTube, video_id: str, filename: str, path: str, is_audio: bool = False) -> None:
diff --git a/pyutube/services/VideoService.py b/pyutube/services/VideoService.py
index 9913d1d..a2cd98d 100644
--- a/pyutube/services/VideoService.py
+++ b/pyutube/services/VideoService.py
@@ -161,42 +161,67 @@ def merging(self, video_name: str, audio_name: str):
         Args:
             video_name: The name of the video file.
             audio_name: The name of the audio file.
-            video_id: The ID of the video.
 
         Returns:
             None
         """
-
         output_directory = os.path.join(self.path, "output")
         os.makedirs(output_directory, exist_ok=True)
 
-        output_file = os.path.join(
-            output_directory, os.path.basename(video_name))
+        # Output file path
+        output_file = os.path.join(output_directory, os.path.basename(
+            video_name).replace(os.path.splitext(video_name)[1], '.mp4'))
+
+        # Extract base names to match files
+        video_base_name = os.path.splitext(os.path.basename(video_name))[0]
+        audio_base_name = os.path.splitext(os.path.basename(audio_name))[0]
 
-        video_name = os.path.join(self.path, video_name)
-        audio_name = os.path.join(self.path, audio_name)
+        # Locate the video file
+        video_path = None
+        for file in os.listdir(self.path):
+            file_base, _ = os.path.splitext(file)
+            if file_base == video_base_name:
+                video_path = os.path.join(self.path, file)
+                break
+
+        if video_path is None:
+            error_console.print(f"❗ Video file not found: {video_name}")
+            sys.exit()
+
+        # Locate the audio file
+        audio_path = None
+        for file in os.listdir(self.path):
+            file_base, _ = os.path.splitext(file)
+            if file_base == audio_base_name:
+                audio_path = os.path.join(self.path, file)
+                break
+
+        if audio_path is None:
+            error_console.print(f"❗ Audio file not found: {audio_name}")
+            sys.exit()
 
+        # Merge video and audio
         ffmpeg_merge_video_audio(
-            video_name,
-            audio_name,
+            video_path,
+            audio_path,
             output_file,
             vcodec='copy',
             acodec='copy',
             ffmpeg_output=False,
-            logger=None
+            logger=None,
         )
 
         # Remove original files
-        os.remove(video_name)
-        os.remove(audio_name)
+        os.remove(video_path)
+        os.remove(audio_path)
 
         # Move the merged file to the current directory
         if os.path.exists(output_file):
-            os.replace(output_file, os.path.join(os.getcwd(), video_name))
+            merged_file_name = os.path.basename(video_name)
+            os.replace(output_file, os.path.join(os.getcwd(), merged_file_name))
             os.rmdir(output_directory)
         else:
-            error_console.print(
-                "Merged video file not found in the output directory.")
+            error_console.print("❗ Merged video file not found in the output directory.")
 
     @staticmethod
     def get_video_resolutions_sizes(
diff --git a/pyutube/utils.py b/pyutube/utils.py
index 63eeb07..4407ca7 100644
--- a/pyutube/utils.py
+++ b/pyutube/utils.py
@@ -16,7 +16,7 @@
 from pytubefix import __version__ as pytubefix_version
 
 
-__version__ = "1.3.39"
+__version__ = "1.4.0"
 __app__ = "pyutube"
 ABORTED_PREFIX = "Aborted"
 CANCEL_PREFIX = "Cancel"