gstreamer1-gst-libav

• If not done already, install MacPorts.
• To install gstreamer1-gst-libav, run the following command in macOS terminal (Applications->Utilities->Terminal)
  
  sudo port install gstreamer1-gst-libav Copy
• To see what files were installed by gstreamer1-gst-libav, run:
  
  port contents gstreamer1-gst-libav Copy
• To later upgrade gstreamer1-gst-libav, run:
  
  sudo port selfupdate && sudo port upgrade gstreamer1-gst-libav Copy

The MacPorts Project uses a system called Trac to file tickets to report bugs and enhancement requests. Though anyone may search Trac for tickets, you must have a GitHub account in order to login to Trac to create tickets.