While so far it worked, we are about to introduce a format that break this assuming. We have a format which consist of NV12 with alpha, and this format does not have a direct mapping of the component against their plane indexes. Fix this by using gst_video_format_info_component() introduced in 1.18 for this purpose. Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/1151>