Subclasses that don't implemen transform_size should be assumed to produce output
buffers of the same size.
https://bugzilla.gnome.org/show_bug.cgi?id=621334
/* if there is a custom transform function, use this */
ret = klass->transform_size (trans, direction, caps, size, othercaps,
othersize);
+ } else if (klass->get_unit_size == NULL) {
+ /* if there is no transform_size and no unit_size, it means the
+ * element does not modify the size of a buffer */
+ *othersize = size;
+ ret = TRUE;
} else {
/* there is no transform_size function, we have to use the unit_size
* functions. This method assumes there is a fixed unit_size associated with