public Caps truncate ()
Discards all but the first structure from this.
Useful when fixating.
This function takes ownership of this and will call
gst_caps_make_writable on it if necessary,
so you must not use this afterwards unless you keep an additional reference to it with
Note that it is not guaranteed that the returned caps have exactly one structure. If this is any or empty caps then the returned caps will be the same and contain no structure at all.
the Caps to truncate