Error is here:
https://github.com/GStreamer/gst-plugins-good/blob/master/sys/v4l2/gstv4l2videodec.c#L960
and here
https://github.com/GStreamer/gst-plugins-good/blob/master/sys/v4l2/gstv4l2videoenc.c#L1046
and here
https://github.com/GStreamer/gst-plugins-good/blob/master/sys/v4l2/gstv4l2transform.c#L1083

static void

gst_v4l2_video_dec_subinstance_init (GTypeInstance * instance, gpointer g_class)

{

  GstV4l2VideoDecClass *klass = GST_V4L2_VIDEO_DEC_CLASS (g_class);

  GstV4l2VideoDec *self = GST_V4L2_VIDEO_DEC (instance);

  GstVideoDecoder *decoder = GST_VIDEO_DECODER (instance);

 

  gst_video_decoder_set_packetized (decoder, TRUE);

 

  self->v4l2output = gst_v4l2_object_new (GST_ELEMENT (self),

      GST_OBJECT (GST_VIDEO_DECODER_SINK_PAD (self)),

      V4L2_BUF_TYPE_VIDEO_OUTPUT, klass->default_device,

      gst_v4l2_get_output, gst_v4l2_set_output, NULL);

  self->v4l2output->no_initial_format = TRUE;

  self->v4l2output->keep_aspect = FALSE;

 

  self->v4l2capture = gst_v4l2_object_new (GST_ELEMENT (self),

      GST_OBJECT (GST_VIDEO_DECODER_SRC_PAD (self)),

      V4L2_BUF_TYPE_VIDEO_CAPTURE, klass->default_device,

      gst_v4l2_get_input, gst_v4l2_set_input, NULL);

  self->v4l2capture->no_initial_format = TRUE;

  self->v4l2output->keep_aspect = FALSE;

}

Look at last code line. It accesses v4l2output instead of v4l2capture.
v4l2output makes no sense, because keep_aspect in v4l2output was already initialized in previous section. This section works on v4l2capture.
I think it is a cut & paste error.