Gets private data set on the picture via gst_mpeg2_picture_set_user_data() previously.
Sets user_data
on the picture and the #GDestroyNotify that will be called when
the picture is freed.
If a user_data
was previously set, then the previous set notify
will be called
before the user_data
is replaced.
a #GDestroyNotify
Create new #GstMpeg2Picture
Create new #GstMpeg2Picture