Dynamic Controllable Parameters Getting Started The controller subsystem offers a lightweight way to adjust gobject properties over stream-time. Normaly these properties are changed using g_object_set(). Timing those calls reliably so that the changes affect certain stream times is close to impossible. The controller takes time into account. It works by attaching control-sources to properties. Control-sources can provide new values for the properties for a given timestamp. At run-time the elements continously pull values changes for the current stream-time. GStreamer includes a few different control-sources, but applications can define their own by subclassing. This subsystem is contained within the gstcontroller library. You need to include the header in your application's source file: ... #include <gst/gst.h> #include <gst/controller/gstcontroller.h> ... Your application should link to the shared library gstreamer-controller. The gstreamer-controller library needs to be initialized when your application is run. This can be done after the GStreamer library has been initialized. ... gst_init (&argc, &argv); gst_controller_init (&argc, &argv); ... Setting up parameter control The first step is to select the parameters that should be controlled. This returns a controller object that is needed to further adjust the behaviour. controller = gst_object_control_properties(object, "prop1", "prop2",...); Next we attach a control-source to each parameter. Lets use an interpolation control-source: csource = gst_interpolation_control_source_new (); gst_interpolation_control_source_set_interpolation_mode(csource, GST_INTERPOLATE_LINEAR); This control-source takes new property values from a list of time-stamped parameter changes. The source can e.g. fill gaps by smoothing parameter changes. This behaviour can be configured by setting the interpolation-mode. Now we can set some control points. These are time-stamped GValues. The values become active when the timestamp is reached. They still stay in the list. If e.g. the pipeline runs a loop (using a segmented seek), the control-curve gets repeated as well. Other control-sources have different functions to specify the control-changes over time. gst_interpolation_control_source_set (csource, 0 * GST_SECOND, value1); gst_interpolation_control_source_set (csource, 1 * GST_SECOND, value2); Finally we need to assign the control-source to the gobject property. One control source can only be assigned to one property. gst_controller_set_control_source (controller, "prop1", csource); Now everything is ready to play. One final note - the controller subsystem has a builtin live-mode. Even though a property has a control-source assigned one can change the GObject property through the g_object_set(). This is highly useful when binding the GObject properties to GUI widgets. When the user adjusts the value with the widget, one can set the GObject property and this remains active until the next programmed control-source value overrides it. This also works with smoothed parameters. It might not work for control-sources that constantly update the property (e.g. the lfo control-source).