public bool set_caps
Sets the capabilities of this pad.
The caps must be fixed. Any previous caps on the pad will be unreffed. This function refs the caps so you should unref if as soon as you don't
need it anymore. It is possible to set NULL caps, which will make the pad unnegotiated again.
|TRUE if the caps could be set. FALSE if the caps were not fixed or bad parameters were provided to this function. MT safe.