Converts caps to a string representation. This string representation
can be converted back to a gstreamer.Caps by Caps.fromString.
For debugging purposes its easier to do something like this:
GST_LOG ("caps are %" GST_PTR_FORMAT, caps);
his prints the caps in human readable form.
The current implementation of serialization will lead to unexpected results
when there are nested gstreamer.Caps / gstreamer.Structure deeper than one level.
a newly allocated string representing caps.