diff --git a/core/video_processing.py b/core/video_processing.py
index 1344a78..f04870d 100644
--- a/core/video_processing.py
+++ b/core/video_processing.py
@@ -1,11 +1,4 @@
-"""
-This module contains functions for processing videos.
-
-Functions:
-    resize_video(video_path, output_video_path, width, height):
-"""
-
-from moviepy.editor import VideoFileClip
+from moviepy.editor import VideoFileClip, TextClip, CompositeVideoClip
 
 def resize_video(video_path, output_video_path, width, height):
     """
@@ -26,3 +19,50 @@ def resize_video(video_path, output_video_path, width, height):
     resized_video.close()
     video.close()
     return output_video_path
+
+def add_watermark(video_path, watermark_text, output_video_path, position=('right', 'bottom')):
+    """
+    Adds a watermark to the input video at the specified position.
+
+    Parameters:
+        video_path (str): Path to the original video file.
+        watermark_text (str): Text to be used as the watermark.
+        output_video_path (str): Path to save the watermarked video.
+        position (tuple): Position of the watermark ('left', 'right', 'top', 'bottom').
+
+    Returns:
+        str: Path to the watermarked video.
+    """
+    video = VideoFileClip(video_path)
+
+    watermark = TextClip(
+        watermark_text,
+        fontsize=24,
+        color='white',
+        font='Arial',
+        stroke_color='black',
+        stroke_width=1,
+        method='caption'  
+    ).set_duration(video.duration).set_opacity(0.6)
+
+
+    if position == ('right', 'bottom'):
+        watermark = watermark.set_position(("right", "bottom"))
+    elif position == ('left', 'bottom'):
+        watermark = watermark.set_position(("left", "bottom"))
+    elif position == ('right', 'top'):
+        watermark = watermark.set_position(("right", "top"))
+    elif position == ('left', 'top'):
+        watermark = watermark.set_position(("left", "top"))
+    else:
+        watermark = watermark.set_position(("center", "center"))
+
+    watermarked_video = CompositeVideoClip([video, watermark])
+
+
+    watermarked_video.write_videofile(output_video_path, codec='libx264', audio_codec='aac')
+
+
+    video.close()
+    watermarked_video.close()
+    return output_video_path
diff --git a/tests/test_video_processing.py b/tests/test_video_processing.py
index 8945e61..e35fd4e 100644
--- a/tests/test_video_processing.py
+++ b/tests/test_video_processing.py
@@ -1,29 +1,41 @@
-'''
-This file contains the unit tests for the video_processing module.
-'''
-
 import unittest
 import os
-from core.video_processing import resize_video
+from core.video_processing import resize_video, add_watermark
 
 class TestVideoProcessing(unittest.TestCase):
-    '''Test cases for the video processing functions.'''
+   '''Test cases for the video processing functions.'''
+
+
+   def setUp(self):
+       self.video_path = os.path.abspath("tests/files/test_video.mp4")
+       self.output_video_path = os.path.abspath("tests/files/resized_test_video.mp4")
+       self.watermarked_video_path = os.path.abspath("tests/files/watermarked_test_video.mp4")
+       self.width = 640
+       self.height = 360
+       self.watermark_text = "KieuHoaB2111982"
+
+
+   def test_resize_video(self):
+       '''Test the resize_video function.'''
+       result_path = resize_video(self.video_path, self.output_video_path, self.width, self.height)
+       self.assertEqual(result_path, self.output_video_path)
+       self.assertTrue(os.path.exists(result_path))
+
 
-    def setUp(self):
-        self.video_path = "tests/files/test_video.mp4"
-        self.output_video_path = "tests/files/resized_test_video.mp4"
-        self.width = 640
-        self.height = 360
+   def test_add_watermark(self):
+       '''Test the add_watermark function.'''
+       # Thêm watermark vào video đã resize
+       result_path = add_watermark(self.output_video_path, self.watermark_text, self.watermarked_video_path)
+       self.assertEqual(result_path, self.watermarked_video_path)
+       self.assertTrue(os.path.exists(result_path))
 
-    def test_resize_video(self):
-        '''Test the resize_video function.'''
-        result_path = resize_video(self.video_path, self.output_video_path, self.width, self.height)
-        self.assertEqual(result_path, self.output_video_path)
-        self.assertTrue(os.path.exists(result_path))
 
-    def tearDown(self):
-        if os.path.exists(self.output_video_path):
-            os.remove(self.output_video_path)
+#    def tearDown(self):
+#        '''Log output file status but do not delete it.'''
+#        if os.path.exists(self.output_video_path):
+#            print(f"[INFO] Output video '{self.output_video_path}' đã được tạo mới.")
+#        if os.path.exists(self.watermarked_video_path):
+#            print(f"[INFO] Watermarked video '{self.watermarked_video_path}' đã được tạo mới.")
 
 if __name__ == "__main__":
-    unittest.main()
+   unittest.main()