avdec_h264 can't decide on src caps

[Klaas Jan Russcher]

I have written an pipeline in C++ that is supposed to show a video, but it
doesn't. The structure of the pipeline is:
appsrc ! VIDEO_CAPS ! rtpstreamdepay ! rtpjitterbuffer ! rtph264depay !
h264parse ! queue ! avdec_h264 ! autovideoconvert ! autovideosink
where VIDEO_CAPS is defined by:
"application/x-rtp-stream, media=(string)video, clock-rate=(int)90000,
encoding-name=(string)H264, packetization-mode=(string)1,
profile-level-id=(string)42c01f,
sprop-parameter-sets=(string)\"Z0LAH9oBQBbsBEAAAAMAQAAADyPGDKg\\=\\,aM48gA\\=\\=\",
payload=(int)96"

The buffers that are put into appsrc (with gst_app_src_push_buffer()) are
extracted from another pipeline:
v4l2src ! queue ! x264enc ! queue ! h264parse ! rtph264pay ! rtpstreampay !
appsink
VIDEO_CAPS of the first pipeline is set to the caps of the sample that is
read from appsink.

To analyse the pipeline I have extracted the graph of the pipeline with
gst_debug_bin_to_dot_file(). It shows that avdec_h264 and autovideoconvert
are connected via "video/x-raw format: { I420, YUY2, RGB, B... }" and "ANY"
caps.
When I remove autovideoconvert, the problem remains. Terminal output with
GST_DEBUG=4 gives (data.video_dec=avdec_h264,
data.video_convert=autovideoconvert):
0:00:00.026803608 31969      0x1675800 INFO   
            GST_PADS
gstpad.c:3995:gst_pad_peer_query:<data.video_dec:src> pad has no peer
0:00:00.026872390 31969      0x1675800 INFO   
            GST_PADS
gstpad.c:3995:gst_pad_peer_query:<data.video_dec:src> pad has no peer
0:00:00.026910994 31969      0x1675800 INFO   
    GST_ELEMENT_PADS
gstutils.c:1571:gst_element_link_pads_full: trying to link element
data.video_dec:(any) to element data.video_convert: any)
0:00:00.026918387 31969      0x1675800 INFO   
            GST_PADS gstutils.c:932:gst_pad_check_link:
trying to link data.video_dec:src and data.video_convert:sink
0:00:00.026929181 31969      0x1675800 INFO   
            GST_PADS
gstpad.c:3995:gst_pad_peer_query:<sink:proxypad0> pad has no peer
0:00:00.026935488 31969      0x1675800 INFO   
            GST_PADS
gstutils.c:1444:prepare_link_maybe_ghosting: data.video_dec and
data.video_convert in same bin, no need for ghost pads
0:00:00.026943286 31969      0x1675800 INFO   
            GST_PADS gstpad.c:2234:gst_pad_link_prepare:
trying to link data.video_dec:src and data.video_convert:sink
0:00:00.026952808 31969      0x1675800 INFO   
            GST_PADS
gstpad.c:3995:gst_pad_peer_query:<sink:proxypad0> pad has no peer
0:00:00.026958722 31969      0x1675800 INFO   
            GST_PADS gstpad.c:2440:gst_pad_link_full:
linked data.video_dec:src and data.video_convert:sink, successful
0:00:00.026964302 31969      0x1675800 INFO   
           GST_EVENT
gstevent.c:1374:gst_event_new_reconfigure: creating reconfigure event
0:00:00.026968753 31969      0x1675800 INFO   
           GST_EVENT
gstpad.c:5499:gst_pad_send_event_unchecked:<data.video_dec:src>
Received event on flushing pad. Discarding

My question is, what causes this problem and how can I solve it? I would
rather not force caps between avdec_h264 and autovideoconvert, because that
undermines the idea of autovideoconvert.
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