Bird tracking and counting -- 2

I am looking for a computer vision expert. I need to count the number of birds going inside the chimney and the number of birds flying out of chimney from the video.

I do not have access to the actual video but you can consider something like this video: https://www.youtube.com/watch?v=he7AJDNjtCc

The accuracy is very important for me. 5- 10 percent maximum error.