Set timestamp and duration to GST_CLOCK_TIME_NONE unless trim==0, because that function doesn't know the rate and therefore can't calculate them. Set offset and offset_end to appropriate values. Make it clear in the documentation that the caller is responsible for setting the timestamp and duration. Fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/issues/869 Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/1039>