Return parent element for a new `p:video` child element.

        The `p:video` element causes play controls to appear under a video
        shape (pic shape containing video). There can be more than one video
        shape on a slide, which causes the precondition to vary. It needs to
        handle the case when there is no `p:sld/p:timing` element and when
        that element already exists. If the case isn't simple, it just nukes
        what's there and adds a fresh one. This could theoretically remove
        desired existing timing information, but there isn't any evidence
        available to me one way or the other, so I've taken the simple
        approach.

def get_or_add_childTnLst(self):
        """Return parent element for a new `p:video` child element.

        The `p:video` element causes play controls to appear under a video
        shape (pic shape containing video). There can be more than one video
        shape on a slide, which causes the precondition to vary. It needs to
        handle the case when there is no `p:sld/p:timing` element and when
        that element already exists. If the case isn't simple, it just nukes
        what's there and adds a fresh one. This could theoretically remove
        desired existing timing information, but there isn't any evidence
        available to me one way or the other, so I've taken the simple
        approach.
        """
        childTnLst = self._childTnLst
        if childTnLst is None:
            childTnLst = self._add_childTnLst()
        return childTnLst