Because we treat raw audio chunks/samples as keyframes, they were interfering with seek time adjustment. Became apparent when the accompanying video stream was I-frame only, for example ProRes. Since raw audio streams can be seeked freely, it's fine to just ignore them here, giving priority to the real keyframes in the video stream. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4946>