In [this video][1] at the 2:40 minute mark there is a relatively clear image of the rear of a Blackbird.  This is a new view - at least for me. Are those "ports" and, if so, what are they venting?  IF not, what are they?

Here is a snapshot at roughly that time:
[![enter image description here][2]][2]


  [1]: https://youtu.be/Tnda8IVqkyI?t=165
  [2]: https://i.sstatic.net/xMSjf.png