try space

app.py

@@ -67,6 +67,6 @@ async def Video(video_file: UploadFile = File(...),kind_back: str = Form(...), b
 
         produced_video=SegmenterBackground().Back_video(video_path, '/tmp/29_sep_2.avi','cam',['animal','person'])#video,background_image,what_remove,blur_radius=23)
         
-        return StreamingResponse(open('/tmp/29_sep_2.avi', "rb"), media_type="video/mp4")
+        return StreamingResponse(open('/tmp/29_sep_2.avi', "rb"), media_type="video/avi")