Example added to the core repo causes no element "filesrc" error

For debugging, I’m adding my own example gstreamer/subprojects/gst-examples/webrtc/sendonly2/meson.build. My build file is

executable('webrtc-sendonly-h264',
           ['webrtc-sendonly-h264.c', 'server/gstreamer_pipeline.c', 'server/signaling_server.c'],
            dependencies : [gst_dep, gstsdp_dep, gstwebrtc_dep, libsoup_dep, json_glib_dep])

When I run it, I got

0:00:00.000442998 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:665:gst_parse_element_make: no element "filesrc"
0:00:00.000459875 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:665:gst_parse_element_make: no element "decodebin"
0:00:00.000464315 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:1385:priv_gst_parse_yyparse: link has no source [sink=@(nil)]
0:00:00.000468354 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:665:gst_parse_element_make: no element "queue"
0:00:00.000471343 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:1385:priv_gst_parse_yyparse: link has no source [sink=@(nil)]
0:00:00.000474845 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:665:gst_parse_element_make: no element "videoconvert"
0:00:00.000477568 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:1385:priv_gst_parse_yyparse: link has no source [sink=@(nil)]
0:00:00.000489999 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:665:gst_parse_element_make: no element "queue"
0:00:00.000492487 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:1385:priv_gst_parse_yyparse: link has no source [sink=@(nil)]
0:00:00.000498340 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:665:gst_parse_element_make: no element "x264enc"
0:00:00.000501105 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:1385:priv_gst_parse_yyparse: link has no source [sink=@(nil)]
0:00:00.000505611 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:665:gst_parse_element_make: no element "queue"
0:00:00.000508003 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:1385:priv_gst_parse_yyparse: link has no source [sink=@(nil)]
0:00:00.000511144 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:665:gst_parse_element_make: no element "h264parse"
0:00:00.000513537 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:1385:priv_gst_parse_yyparse: link has no source [sink=@(nil)]
0:00:00.000517646 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:665:gst_parse_element_make: no element "rtph264pay"
0:00:00.000519966 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:1385:priv_gst_parse_yyparse: link has no source [sink=@(nil)]
0:00:00.000524912 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:665:gst_parse_element_make: no element "tee"
0:00:00.000527235 1619980 0x6384e9e65af0 ERROR           GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:1385:priv_gst_parse_yyparse: link has no source [sink=@(nil)]

Any idea? Thanks!

Not only my custom example but also the official examples don’t work. It always says no element "xxx"