why rtspclientsink can not work with vaapioverlay?

[criusxu]

I am using  the last gstreamer and gstreamer-vaapi .
this pipeline is woke fine 

gst-launch-1.0  v4l2src  device=/dev/video0  !   video/x-raw, width=1920,
height=1080 ! \
   vaapih264enc ! \
rtspclientsink debug=1 latency=0 location=rtsp://127.0.0.1:554/mystream

but when i add the vaapioverlay element ,it can note work.

gst-launch-1.0  v4l2src  device=/dev/video0  !   video/x-raw, width=1920,
height=1080 ! \
 vaapioverlay !   vaapih264enc ! \
rtspclientsink debug=1 latency=0 location=rtsp://127.0.0.1:554/mystream


report this  error:
../subprojects/gstreamer/libs/gst/base/gstbasesrc.c(3127): gst_base_src_loop
(): /GstPipeline:pipeline0/GstV4l2Src:v4l2src0:
streaming stopped, reason not-negotiated (-4)


any help is appreciate !





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