I'd like to learn the gstreamer media framework. Where should I start?
The homepage has a section for developers: http://gstreamer.freedesktop.org/dev/
They point to reading the manuals as a good place to start.
The Gstreamer Application Development Manual is an excellent place to start. It gives you a nice introduction to Gstreamer as well as some nice code examples. I would also recommend looking at some of the examples provided int the gstreamer source tree. Those will also be very helpful in understanding how gstreamer works.
In general all of the Gstreamer documentation is very good.
The other nice thing about gstreamer as a media API is that there are a whole host of open source applications that you can look at for example implementations. If you are interested using gstreamer for audio I would recommend checking out the Banshee or Songbird source code. If you are interested in video check out the Totem or Pitivi source.
Starting with python is a good startpoint since is a little bit more simplified. I suggest you to check this tutorial
You won't get far without joining the gstreamer mailing list:
https://lists.sourceforge.net/lists/listinfo/gstreamer-devel
as it seems the developers prefer to answer questions over and over again instead of producing useful documentation.
You'll also need to download the source code and search through it for examples that unfortunately range from useless to very helpful with precious little guidance.
If you don't fully understand the GObject system (why use C++ when you can reinvent it badly, not that I'm a fan of C++) you are basically dead until you do.
I found the book "Foundations of GTK+ Development" by Andrew Kruase invaluable.
There is a pretty good archive of the gstreamer mailing list at nabble.com, sorry don't have a link handy.