diff --git a/demo/video_matting/offline/requirements.txt b/demo/video_matting/offline/requirements.txt
new file mode 100644
index 0000000..44c4e44
--- /dev/null
+++ b/demo/video_matting/offline/requirements.txt
@@ -0,0 +1,6 @@
+numpy
+Pillow
+opencv-python
+torch >= 1.0.0
+torchvision
+tqdm
\ No newline at end of file
diff --git a/demo/video_matting/offline/run.py b/demo/video_matting/offline/run.py
index 0e3f061..e2d18ea 100644
--- a/demo/video_matting/offline/run.py
+++ b/demo/video_matting/offline/run.py
@@ -36,7 +36,7 @@ else:
 modnet.eval()
 
 
-def offline_matting(video_path, save_path, fps=30):
+def offline_matting(video_path, save_path, alpha_matte=False, fps=30):
     # video capture
     vc = cv2.VideoCapture(video_path)
 
@@ -53,7 +53,7 @@ def offline_matting(video_path, save_path, fps=30):
     h, w = frame.shape[:2]
 
     # video writer
-    fourcc = cv2.VideoWriter_fourcc('M', 'J', 'P', 'G')
+    fourcc = cv2.VideoWriter_fourcc(*'mp4v')
     video_writer = cv2.VideoWriter(save_path, fourcc, fps, (w, h))
 
     print('Start matting...')
@@ -61,7 +61,6 @@ def offline_matting(video_path, save_path, fps=30):
         for c in t:
             frame_np = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
             frame_np = cv2.resize(frame_np, (672, 512), cv2.INTER_AREA)
-            # frame_np = frame_np[:, 120:792, :]
 
             frame_PIL = Image.fromarray(frame_np)
             frame_tensor = torch_transforms(frame_PIL)
@@ -74,30 +73,34 @@ def offline_matting(video_path, save_path, fps=30):
 
             matte_tensor = matte_tensor.repeat(1, 3, 1, 1)
             matte_np = matte_tensor[0].data.cpu().numpy().transpose(1, 2, 0)
-            fg_np = matte_np * frame_np + (1 - matte_np) * np.full(frame_np.shape, 255.0)
-            fg_np = cv2.cvtColor(fg_np.astype(np.uint8), cv2.COLOR_RGB2BGR)
-            fg_np = cv2.resize(fg_np, (w, h))
+            if alpha_matte:
+                view_np = matte_np * np.full(frame_np.shape, 255.0)
+            else:
+                view_np = matte_np * frame_np + (1 - matte_np) * np.full(frame_np.shape, 255.0)
+            view_np = cv2.cvtColor(view_np.astype(np.uint8), cv2.COLOR_RGB2BGR)
+            view_np = cv2.resize(view_np, (w, h))
+            video_writer.write(view_np)
 
-            video_writer.write(fg_np)
             rval, frame = vc.read()
             c += 1
 
     video_writer.release()
-    print('Save video to {}'.format(args.save_path))
+    print('Save video to {}'.format(save_path))
     return
 
 
 if __name__ == "__main__":
     parser = argparse.ArgumentParser()
     parser.add_argument('--video_path', type=str, default='./sample/video.mp4')
-    parser.add_argument('--save_path', type=str, default='./sample/matte.mp4')
+    parser.add_argument('--save_path', type=str, default='./sample/res.mp4', help='Video should be .mp4 format.')
+    parser.add_argument('--alpha_matte', action='store_true', default=False, help='If True, save alpha_matte video.')
     parser.add_argument('--fps', type=int, default=30)
 
     args = parser.parse_args()
 
-    if not args.save_path.endswith('avi'):
-        args.save_path = os.path.splitext(args.save_path)[0] + '.avi'
+    if not args.save_path.endswith('.mp4'):
+        args.save_path = os.path.splitext(args.save_path)[0] + '.mp4'
 
-    offline_matting(args.video_path, args.save_path, args.fps)
+    offline_matting(args.video_path, args.save_path, args.alpha_matte, args.fps)