If @prefer_passthrough is %TRUE (the default), @trans will check and
prefer passthrough caps from the list of caps returned by the
transform_caps vmethod.
If set to %FALSE, the element must order the caps returned from the
transform_caps function in such a way that the preferred format is
first in the list. This can be interesting for transforms that can do
passthrough transforms but prefer to do something else, like a
capsfilter.
If @prefer_passthrough is %TRUE (the default), @trans will check and prefer passthrough caps from the list of caps returned by the transform_caps vmethod.
If set to %FALSE, the element must order the caps returned from the transform_caps function in such a way that the preferred format is first in the list. This can be interesting for transforms that can do passthrough transforms but prefer to do something else, like a capsfilter.
MT safe.