GStreamer is an open source media handling library. It allows Transcribe! to:
With Transcribe! version 9.1 or later we include GStreamer as part of the Transcribe! download for Windows and Mac. On Linux you have to have GStreamer already installed.
You can always check whether GStreamer is installed correctly by looking at Transcribe!'s "System Info" command (on the Application menu or the Help menu) where you will find a message about GStreamer.
GStreamer is "free" sofware, both in the sense that you can download the source code if you want to, and in the sense that it doesn't cost any money. If you want to know more about GStreamer, you can find their home page here.
If you are running an older version of Transcribe! and are seeing messages about how you need GStreamer, then you should update to the latest version of Transcribe! that you can run, free to existing users, see here. If you cannot update to version 9 Transcribe! then see here.