I haven't managed to solve the installation issues of GSVideo on OSX yet. So you might want to try out the JMCVideo library, which is a good option for playback.
If you want to stick to GSVideo and don't have administrator access, all I can suggest at this point is the following:
1) grab the latest version of gsvideo:
https://sourceforge.net/projects/gsvideo/files/gsvideo/0.6/gsvideo-0.6-pre0.zip/...and install in the libraries folder as usual.
2) download the zip file I made of the gstreamer binaries for osx
https://sourceforge.net/projects/gsvideo/files/gsvideo/0.5/GStreamer-MacBuild-0....and uncompress somewhere in the hard drive.
3) grab the following startup script
https://sourceforge.net/projects/gsvideo/files/gsvideo/0.5/p5-gsvideo.sh/downloa... First, make sure it is executable (open a terminal, change to the directory where you copied the script and run: "chmod +x p5-gsvideo.sh"). Also, edit the script (with any text editor), to set the correct locations of the gstreamer files depending on where you installed them in step
2. Then you can run processing with gsvideo/gstreamer support by executing the script from the terminal
It is not very nice, unfortunately gsvideo/gstreamer integration with osx is poor at this point. I hope this helps.