The GStreamer properties applet offers four drop down menus spread over two tabs. There are two drop-menues for audio and two for video. These choices set the default for most GNOME applications for output and input of Sound and Video.

3.1. Understanding the menu options

Looking at the screen for setting audio options you notice that the two sections are called Default Sink and Default Source. These are terms used in the GStreamer framework that GNOME uses to describe where data is sent and where it comes from. The Default sink is in other words where GNOME apps should output their sound, while Default source is where the sound comes from.

The reason you might want to alter these settings is because under Unix there are many different audio systems and sound server which you might want to output to. For instance on Linux popular alternatives are the PulseAudio sound server or ALSA.

If you wish that your GNOME applcations output their sound to the PulseAudio sound server you set the Default Sink to use PulseAudio. And if you wish that your GNOME applications which has sound recording capabilities use the ALSA sound system, choose ALSA as the Default Source.

As mentioned elsewhere in this user guide. These setting are meant for as a tool for advanced users who have specialized need. As an ordinary user, you should not need to set these as the vendor of your distribution should have set them to sensible defaults for you.